Safety Treatment of Roadside Drainage Structures

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SAFETY TREATMENT OF ROADSIDE DRAINAGE STRUCTURES

by

Hayes E. Ross, Jr. Dean Sicking T. J. Hirsch

Texas Transportation Institute

Harold D. Cooner John F. Nixon Samuel V. Fox

Texas State Department of Highways and Public Transportation

C. P. Damon Federal Highway Administration

Submitted to

TRB Committee A2A04 for

review and possible presentation and publication by TRB

August, 1981

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H. E. Ross, et al 1

ABSTRACT

The purpose of the research was to develop traffic-safe end treatments

for (1) cross-drainage structures and (2) parallel-drainage structures that

would not appreciably restrict water flow. Cross-drainage culverts are used

to convey water under the highway. Parallel-drainage culverts are used to

convey water under driveways, side roads, ramps, or median crossovers that

abut the highway.

Preliminary designs were first evaluated by computer simulation, by use

of a test pit in which the clear open space and grate spacing could be var

ied, and by use of an earth berm similar in geometry to a driveway. Prom

ising designs were then subjected to full-scale prototype testing with both

subcompact and full-size automobiles.

Traffic-safe culvert end treatments can be achieved as follows:

Cross-drainage structures - (a) All culvert ends should be made to match the

existing side slope with no protrusion in excess of 4 in. (10.2 cm) above

grade; (b) culverts with clear openings 30 in. (76.2 cm) or less need no

safety treatment other than as mentioned in (a); (c) culverts with clear

openings greater than 30 in. (76.2 cm) can be made traffic-safe by grate mem

bers placed on 30 in. (76.2 cm) centers oriented parallel to the flow and in

the plane of the side slope.

Parallel-drainage structures - (a) The roadway side slope (or ditch slope)

shoul d be 6 to 1 or fl atter in the vi ci ni ty of the dri veway; (b) the dri veway

slope should be 6 to 1 or flatter; (c) the transition between the side slope

and the driveway slope should be rounded; and (d) safety treatment of the

culvert opening should include an end section cut to match the driveway slope

with cross members (grates) spaced every 24 in. (61.0 cm) perpendicular to

the direction of flow.

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H. 1:. KOSS, et al 2

Application of these findings will result in improved safety for the

motorist. They will also result in more hydraulically efficient and more

economical safety treatments than have been used in the past.

I NTROD U cn ON

In designing drainage culverts, the primary objective is to properly

accommodate su rface runoff along the highway ri ght-of-way. However, a second

important goal should be to provide a traffic-safe design that would be tra-

versable by an out-of-control vehicle without rollover or abrupt change in

speed.

Guidelines for designing traffic-safe grates have been very limited.

NCHRP published guidelines for traffic-safe drainage structures in 1969 UJ. The recommendat ions dealt prima ri ly with the geometry of adjoi ni ng slopes.

Computer simulations have also been used to futher investigate the dynamic

behavior of automobiles traversing various slope and ditch configurations

near driveways and median crossovers (1,1). Criteria for the structural de

sign of inlet grates was published in 1973 (1). However, the study did not

address the problem of grate design as related to safety.

Recent field reviews of drainage culverts in Texas revealed that im-

provements and some modification of design details could improve both drain-

age and safety (~). Many of the safety grates used in the past to cover the

open ends of culverts have small openings and the grates are easily clogged

with debris, causing water to back up and flow over the roadway, the ditch

crossing, or adjacent property. In some cases safety grates do not possess

enough strength to be effective or they are used on small pipe culverts which

need no safety treatment.

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H. E. Ross, et al 3

The objective of this study was to develop guidelines for safety treat

ment of both cross-drainage and parallel-drainage structures that (1) can be

safely traversed by an errant vehicle and (2) will exhibit desirable hydrua

lic behavior. Although no hydraulic analyses were made it was assumed that

hydraulic efficiency increases as the number of grate members decrease. It

was therefore a goal of the research to meet safety requirements with as few

grate members as possible.

This paper summarizes the findings of two research studies, one conduc-

ted in 1979 (i) and the other in 1980 (2). Reference should be made to the

cited literature for complete details of the studies.

EVALUATION CRITERIA

A review of the literature showed that there are no nationally recog-

nized safety performance standards for roadside drainage structures. Decele

ration and stability of a vehicle during and following impact are the two

primary measures of performance for safety appurtenances such as guardrail s,

crash cushions, etc. (~). For the cross-drainage structures, performance was

judged satisfactory if the vehicle smoothly traversed the culvert and the ad

joining ditch slope without rollover for speeds from 20 mph (32.2 km/h)

through 60 mph (96.5 km/h).

Previous research (£&) indicated that a very flat ditch slope, a very

flat driveway slope, and a very long culvert would be necessary to satisfy

the above criteria for parallel-drainage structures. In view of the economic

and hydraul i c imp 1 i cat ions of such a desi gn it was conc 1 uded that tradeoffs

would be necessary to achieve an acceptable balance between the controlling

elements. Performance of parallel-drainage structures was therefore judged

acceptable if the vehicle smoothly traversed the adjoining slopes and culvert

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H. E. Ross, et al 4

without rollover for speeds from 20 mph (32.2 km/h) through 50 mph (96.5

km/h) •

RESEARCH APPROACH

A three-phase approach was taken in the development of safety treatments

of both cross-drainage and parallel-drainage structures. In the first two

phases computer simulations in combination with a preliminary test program

were used to develop tentative design concepts. In the latter phase proto-

types were constructed using the rl'!sults of the preliminary studies and

tested under representative roadside configurations.

Cross-Drainage Structures

Simulation studies - A computer simulation study was conducted, using

the Highway-Vehic1e-Object-Simu1ation-Mode1 (HVOSM) (1) , to evaluate wheel

drop into various culvert openings on flat terrain. HVOSM was also used to

investigate the effect a ramp at the leading edge of the culvert opening

would have on vehicle behavior. Ramps having the following dimensions were

eva 1 uated:

Hori zonta 1 Ve rt i ca 1

Ramp Dimension (i n.) Dimension (in.)

1 3.0 3.0

2 6.0 3.0

3 6.0 6.0

4 12.0 6.0

A 1974 Honda Civic was simulated in each of the computer runs since it was

assumed a mini-size automobile would be more critical than a larger vehicle

for the given conditions. A speed of 20 mph (32.2 km/h) was used in each run

since it was deemed a critical speed. At higher speeds it was felt the

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H. E. Ross, et al 5

vehicle would clear the opening easier. At lower speeds, although the vehi

cle would tend to drop more, velocity changes would be tolerable.

Preliminary tests - In the second phase a test pit was constructed on

flat terrain as shown in Figure 1 to study the behavior of a vehicle as it

traversed various openings. The objectives of these tests were to determine

preliminary values for (1) the maximum clear opening permissible on a non-

grated culvert end and (2) the maximum spacing permissible when grates are

necessary. All runs were live-driver tests at various speeds and encroach-

ment angles. Figure 2 is a photograph of the test pit after installation. A

total of 31 runs were made to determine the maximum clear opening. Test

speeds ranged from 5 mph (8.0 km/h) to 35 mph (56.3 km/h);encroachment angles

varied from 0 degrees to 15 degrees; and clear openings ranged from 12 in.

(30.5 cm) to 36 in. (91.4 cm). All tests were with a 1974 Honda Civic having

a curb weight of approximately 1800 lb (817.2 kg). Limiting values were

determined by the severity of the ride as judged by the driver. The driver

was a Texas Transportation Institute (TTl) technician with a nonprofessional

driving history. Sequential photos of a 20 mph (32.2 km/h) run with a 30

in. (76.2 cm) clear opening are shown in Figure 3.

Upon completion of the clear opening tests the pit was used to determine

maximum permissible grate spacing. A total of 22 live-driver tests were con-

ducted for this purpose. Test speeds ranged from 5 mph (8.0 km/h) to 25 mph

(40.2 km/h); encroachment angles varied from 0 degrees to 30 degrees; and

grate spacing varied from 16 in. (40.6 cm) to 30 in. (76.2 cm). The grates

were 3 in. (7.6 cm) schedule 40 steel pipe anchored to a steel beam with pro-

vision to allow adjustments of the pipe to any desired spacing. Figure 4

shows the pit setup for a 16 in. (40.6 cm) grate spacing. Each grate config-

uration was evaluated with the 1974 Honda Civic. A 1975 Plymouth Fury

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10'-0" Clear

Fl at Terra i n~Ii--_.~\' I . "':

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3"<P Std. Pipe Grating; Spacing Varies

Edge of Pavement •... ~ .. (: .. <:; • ...

'. . ' ". ".

18" Deep Concrete Pit

~_ Adjustable Cover Plate to Create Clear Opening

Variable Clear Opening

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Vehicle ~; Encroachment Angle Varies

Figure 1. Plan View of Culvert Test Pit.

ANGLE: IS 5 PEE O:l0l: OPN'G 22 PL,

Figure 2. Test Pit Installation.

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H. E. Ross, et al

0.000' sec.

0.060 sec.

0.135 sec.

ANGLE: 0

SPEEO:20,: OPN°G;J.O Pl.

0.030 sec.

0.105 sec.

Figure 3. Sequential Photos of Nongrated Culvert Test, 30 in. Clear Opening, 1974 Honda Civic

7

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H. t. KOSS, et al

• Figure 4.

"

ANGLE: 0 SPEED:lDf DPN'G,ISPIPE

Test Pit With 16 in. Grate Spacing.

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H. E. Ross, et al 9

weighing about 4500 Ib (2043 kg) was also used to evaluate the larger grate

spadngs.

As part of the second phase of the study a limited number of live-driver

tests were conducted to further evaluate the effects of a ramp at the leading

edge of the cul vert openi ng. Based on the HVOSM results, a ramp with a hori

zontal dimension of 12 in. (30.5 cm) and a vertical dimension of 6 in. (15.2

cm) was selected and constructed. HVOSM indicated this combination would

produce the greatest wheel hop of all combinations considered. The 1974

Honda Civic and the 1975 Plymouth Fury were used in the ramp test. Each test

was conducted at 20 mph (32.2 km/h).

Prototype tests - Based on results obtai ned from the prel imi nary stud

i es, two cul vert structures were constructed for full-scale testing. They

consisted of a 30 in. (76.2 cm) diameter corrugated steel pipe culvert and a

5 ft (1.5 m) wide by 3 ft (0.92 m) high concrete b.ox culvert with adjoining

head and wing walls. Grate members on the box culvert consisted of 3 in.

(7.6 cm) schedule 40 steel pipe on 30 in. (76.2 cm) centers. Photos of both

installations are shown in Figure 5.

General details of the six tests conducted are shown in Figure 6. Note

that the culverts were subjected to tests with both the mini-size and full-

size automobiles. In each test, with the exception of test 5, all four

wheels of the test vehicle crossed the sloped culvert opening. In test 5 the

vehicle straddled the cross member at the end of the box culvert, allowing

the left side wheels to drop approximately 1.5 ft (0.46 m) to the ditch·

bottom. Sequential photos of test 3 are shown in Figure 7.

Analysis of the strength requirements of grate members indicated that a

3 in. (7.6 cm) J.D. schedule 40 pipe was adequate for spans up to 12 ft (3.7

m). Since grate spans on many box culverts would exceed 12 ft (3.7 m) it was

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H. E. Ross, et al 10

a) Corrugated Steel Pipe Culvert.

b) Grated Box Culvert.

Figure 5. Prototype Test Installations.

•

H. E. Ross, et al

Make Model Year Test Weight (1 b) Test No . Velocity (mph)

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VEHICLE DATA

Car 1

Honda CVCC 1974 1800 2, 3, 5 20

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Car 2

Plymouth Fury 1975 4500 1, 4, 6 20, 60

Metric Conversions:

1 lbm = 0.454 kg

1 mph = 1.609 km/h

, . "-:.;.~"~ ." Edge of Run~/ay , ..

):': '. Ditch Front S19pe Approx. 5: 1 J .~ • ,It _. : .. ~~ "

1~~12;-~Pipe Culvert , .

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20 mph, Tests 1 and '.2

Box Culvert with Grating '. '.,

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~vehicles towed with cable

t V = 20 mph, Tests 3', 4, and 5. r-- 60 mph, Test g.

Figure 6 Plan View of Site for Prototype Tests.

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0.000 sec 0.092 sec

0.174 sec 0.353 sec

0.530 sec

Figure 7. Sequential Photos, Test3.

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H. Eo Ros s, et a 1 13

conclude.d that a limited test program should be undertaken to determine pipe

size requirements for larger spans. To accomplish this another test pit was

constructed on flat terrain. The pit was of 20 ft (6.1 m) long, 10 ft (3.1

m) wide, and 1.5 ft (0.46 m) deep. A total of four full-scale vehicular

tests were conducted with a 4500 1b (2043 kg) vehicle, each at 20 mph (32

km/h) and each at a head-on approach, perpendicular to the 20 ft (6.1 m)

dimension of the pit. Further details of each test are given in Table 1, in

cluding the permanent deformations noted after each test. With the exception

of test 4 the grates had a 20 ft (6.1 m) clear span. In test 4, vertical

supports consisting of 3 in. (7.6 cm) 1.0. schedule 40 pipe were placed at

midspan of each of the three grate members. The grates were attached to the

walls of the pit with a pin connection, constructed according to TSDHPT stan

dards.

Parallel-Drainage Structures

Simulation studies - Design of a traffic-safe parallel drainage struc

ture not only involves the culvert itself but adjoining slopes as well. In

fact, the slopes can in many cases be a greater hazard than the culvert

structure. Studi es of medi an cross-over geometry poi nted to the need for re

latively flat slopes to minimize vehicle rollover (~,l). To gain further in

sight, HVOSM was used to examine the behavior of·a vehicle traversing various

driveway conditions. Parameters investigated included departure angle,

departure speed, and the path of vehicle encroachment; the side slopes of

both the ditch and the driveway; the type of transition zone between the two

slopes; depth of the ditch; and vehicle size. These parameters are illus

trated in the definition sketch of Figure 8.

Following is the range of each parameter evaluated:

DEPARTURE ANGLE: .150 and head-on

H. E. Ross, et a1 14

Table 1 . Cross Member Deflections of Box Culvert Grating Strength Tests

TEST PIPEa GRATE EST. NO. 1.0. MEMBERb VERTICAL DEFLECTION HORIZONTAL DEFLECTION

( in. ) (in. ) (in.)

{ First -0 0

1 5 Second -0 0

Third -15/16 3/8

{ First -1/8 0

2 4 Second -1/2 1/4

Third -3 1 7/8

{ First -1 3/4 2 7/8

3 3.5 Second -4 3/4 3 1/16

Third -4 1/8 1 7/16

{ First -0 3/4 1 1/2

4c 3 Second +0 1/2 1 7/8

Third +0 1/8 4 3/4

a. Schedule 40 Steel Pipe.

b. Grate Members Spaced on 30 in. Centers.

c. Midspan Vertical Supports Used On Each Grate.

H. E. Ross, et a1

. SHOULDER

,.;. SIDE

SLOPE)

"--,

. DITCH J

/' I // )-~/~--------~

/ I

/ / / / DRIVEWAY /

/

/~--/~/------------------------~-------4 ( ./

TRANSITI0!;J, ... ~ ./ ZONE SEE DETAILS", a ~ (TYPICAL FOUR , PLACES) ~'----~--------------------~r-----~

DRIVEWAY~

ANGLED PATH (I)

ANGLED PATH (2)

DEPARTURE ANGLE

'~

PLAN VIEW

Figure 8. Definition Sketch

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H. E. Ross, et a1

(

DITCH DEPTH

SECTION ''A-All

SECTION "8-811

LINES OF EQUAL ELEVATION

ABRUPT TRANSITION

DETAIL SMOOTH TRANSITION

DETAIL 2

Figure 8. Definition Sketch (continued)

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ters.

DEPARTURE SPEED: 30 mph (48.3 km/h), 40 mph (64.4 km/h), 50 mph (80.5

km/h), and 60 mph (96.6 km/h)

PATH: 150 angled path across transition (path 1), 150 angled path

across ditch bottom (path 2), and head-on path into driveway

slope (path 3)

ROADWAY SLOPE: 4:1 and 6:1

DRIVEWAY SLOPE: 4:1,5:1, and 6:1

TRANSITION TYPE: Abrupt and rounded

DITCH DEPTH: 2 ft (0.61 m) and 3 ft (0.92 m)

VEHICLE SIZE: 2250 lb (1022 kg) and 4500 lb (2044 kg)

A total of 68 computer runs were made to eva 1 uate the va ri ous pa rame-

Preliminary tests - Ten full-scale vehicular tests were conducted to

(1) evaluate vehicle response as a function of the driveway slope and (2) to

develop a tentative safety treatment for parallel-drainage structures. The

test vehicles were 1974 and 1975 Chevrolet Vegas weighing approximtely 2250

lb (1022 kg). In each test the vehicle was towed to the test site along a

guidance cable, released, and then allowed to traverse the test area in a

free-wheel (no steer input), no-braking mode. A summary of the 10 tests is

given in Table 2, tests 1-1 through 7-6. Tests 1-1 through 5-1 were designed

to evaluate the relative hazard of the driveway slope. An earth berm was

constructed to simulate the driveway. The berm for tests 1-1 through 1-4 had

a 3.8 to 1 slope, was approximately 3 ft (0.92 m) high, and was approximately

20 ft (6.1 m) wide at the top. Sequential photos of test 1-4 are shown in

Figure 9.

After test 1-4 the berm slopes were flattened to the dimensions shown on

the first page of Figure 10. In this case the slope on the approach side was

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6.7 to 1. It was obvious from test 1-3 that an automobile could traverse the

6.7 to 1 slope at speeds in excess of 40 mph (64.4 km/h) without roll i ng

over. Hence, test 5-1 was conducted at 50 mph (80.5 km/h) with the automo

bile approaching from a head-on path. Although the vehicle was airborne for

approximately 75 ft (22.9 m) it remained upright with no appreciable

pitching.

The next seri es of tests (7-1 through 7-6) were conducted to determi ne

if safety treatment of the culvert end was needed in addition to the sloped

end treatment. The 6.7 to 1 driveway slope was used in each test. It was

assumed that a head-on path into the driveway culvert would be as critical,

or more critical, than any other path regarding the culvert itself. Based on

this assumption, a 24 in. (61.0 cm) diameter corrugated steel pipe culvert

with a sloped end was installed in the earth berm as shown on the first page

of Figuere 10. This culvert size was selected since the diameter of most

driveway culverts in Texas are equal to or less than 24 in. (61.0 cm). Vehi

cle impact point for this series of tests was selected such that the right

side wheels of the test vehicle traversed the center of the culvert end.

Details of the culvert configuration for each of the culvert tests are

given in Figure 10. Test 7-1 was conducted at 50 mph (80.5 km/h) with an

open culvert, i.e., no grate members. Photos of the installation are given

in Figure 11 and sequential photos of the test are given in Figure 12. Large

pitch and roll rates occurred after impact with the culvert, and the vehicle

rolled over. In test 7-2 a single grate member was placed across the culvert

as shown in details 3 and 4 of Figure 10. Very little improvement in vehicle

behavior was realized and rollover again occurred.

Analysis of test 7-2 showed that grates spaced approximately on 2 ft

(0.61 m) centers was needed to avoid excessive wheel drop and wheel snagging.


The next treatment therefore incorporated thi s featu re as shown in detail s 5

and 6 of Figure 10. Grate members consisted of 2 lb/ft (2.98 kg/m) steel

flanged channel sections. The channel section was chosen since it is widely

used as a del ineator post by TSDHPT and woul d therefore be readily avail

able. The first test on this treatment, test 7-4, was conducted at 20 mph

(32.2 km/h) and the results were acceptable. Test 7-5 was conducted at 50

mph (80.5 km/h) and rollover occurred due to structural failure of the

grates.

In test 7-6, 2-1/2 in. (6.35 cm) 1.0. standard steel pipe (schedule 40)

were used as a grate member. Details 7 through 10 of Figure 10 show how the

pipe was attached to the culvert. Although .the vehicle was airborne approxi

mately 65 ft (19.8 m) it remained upright and the test was deemed accept

able. The culvert was only slightly damaged.

Prototype tests - The final two tests, 9-1 and 9-2, were selected to

verify the tentative conclusions r.eached as a result of the simulation work

and the full-scale slope and culvert testing. A full-scale prototype of a

ditch-dri veway confi gu rat i on was constructed as shown in Fi gu re 13 and the

photos of Figure 14. Test 9-1 was conducted at 40 mph (64.4 km/h) and the

approach path into the driveway was as shown in Figure 13 such that the left

side wheels crossed the culvert. No adverse vehicle behavior occurred during

the test and the results were considered acceptable.

Test 9-2 was identical to test 9-1 except the speed was increased to 50

mph (80.5 km/h). Sequential photos of the test are shown in Figure 15. The

vehicle remained upright and sustained only minor damage. The culvert was

only slightly damaged and could have been used without repair.

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TABLE 2. SUMMARY OF FULL-SCALE TEST RESULTS

TEST VEHICLE VEHICLE DRIVEWAY DITCH CULVERT NO. SPEED PATH SLOPE SLOPE CONFIGURATION RE SUL TS

(mph) (See Fig. 1) ------- --

1 - 1 30 3 3.8; 1 N/A . No Cu1 vert Satisfactory - no ro1iover

1-2 35 3 3.8; 1 N/A No Culvert Satisfactory - no rollover

1-3 40 3 3.8; 1 N/A No Cu1 vert Satisfactory - no rollover

1-4 50 3 3.8; 1 II/A No Cu1 vert Unsatisfactory - vehicle pitched over

5- 1 50 3 6.7;1 N/A No Cu1 vert Satisfactory - no rollover

7-1 50 3 6.7;1 N/A (See Fig. 10) Unsatisfactory - vehicle rolled over

7-2 50 3 6.7; 1 N/A (See Fig. 10) Unsatisfactory - vehicle rolled over

7-4 20 3 6.7; 1 N/A (See Fig. 10) Satisfactory - no rollover

7-5 50 3 6.7: 1 N/A (See Fig. 10) Unsatisfactory - vehicle rolled over

7-6 50 3 6.7;1 N/A (See Fig. 10) Satisfactory - no rollover

9-1 40 2 6.5;1 6.8: 1 (See Fig. 13) Satisfactory - no rollover

9-2 50 2 6.5; 1 6.8; 1 (See Fig. 13) Satisfactory - no rollover

Metric Conversions: 1 mph = 1.609 km/h

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0.091

0.402

r

1.018

.-, .

1.777

figure 9. Sequential Photos, Test 1-4.

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0.332

I ntr

0.775

1.395

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3 - RAIILRC)AD ____ T1ES--

PLAN ..

22

24'-5"

BERM

FOR TEST 7-1 SEE DETAILS I AND 2 FOR TEST 7-2 SEE DETAILS 3 AND 4 = FOR TEST 7-48& 7-5 SEE DETAILS 5 a 6 I

_~::--~FOR TEST 7-6 SEE DETAILS 7 AND 8 '-t ! =jjll-=i1i~II§ilil;~. i~ 1Ii1- A ltllggojill i ----==J1I1~~-- -. - RAILROAD 1I11'§JlTI -

-Sllil -.. TIES 1111_

SECTION "A II

3/4" GAL\/. CHANNEL I CRIMPED a SPOT WELDED 7'-0· (TYPICAL . TEST) ~;;-:::S-__

t . Ill! llil~- i1 ==.L- 1 = 1 ~\l1

~ .:::::1111=_1 \I llli =

, "2" 7.::oTIlIUIII ~IIII IIIF" DETAIL I

24" OIA. GALV.

~L~~...-lil

ti~~kr:-;-7-:-7· 770'l/ / /./ I' ; I

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CORRUGATED PIPE---

3/4" GAL\/. ANGLE CRIMPED a SPOT WELDED (TYPICAL EA. TEST)

DcTAIL 2

Figure 10. Berm and Culvert Details, Tests 5-1 through 7-6.

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H. E. Ross, et al

7'-0"

===:1\= - Jill

-=D=E=TA:-:I:--L--:3=---:2 1/2" DIA. STEEL .... ,~~'"" (SCHEO. 40)

7'-0·

.:D:E1i::~:;;-;I~L:;5~~ 4 - DELINEATOR POSTS EQUALLY SPACED

NOTE: SEE DETAIL 9 1-____ 8~'-::::.0_., ___ ___I. / FOR WELD LOCATiONs

Figu!'e 10.

=~~t ~/:..--:.---~~ ;

. DETAIL 7

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Berm and Culvert Details, Tests 5-1 through 7-6. 14

23

DETAIL 4

DETAIL 6

DETAIL 8

(continued)

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Figure 10. Berm and Culvert Details. Tests 5-1 through 7-6. (continued) 15

H. E. Ross,et al 25

Figure-ll~ Test Installation Before Test 7-1.

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Figure 12. Sequential Photos, Test 7-1.

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24" DIA. GAL\l CORRUGATED PIPE WITH 4 - 2 1/2" DIA. STEEL. PIPES (SCHED 40)

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Figure 13. Test Site Conditions, Tests 9-1 and 9-2.

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Figure 14. Test Site, Tests 9-1 and 9-2.

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FI ND INGS

Cross-Drainage Structures

Based on the computer simulations and the preliminary test program, it

was shown that clear openings of at least 30 in. (76.2 em) could easily be

tra ve rsed at a speed of 20 mph (32.2 km/h). A 36 in. (91.4 em) spaci ng was

easily traversed at 25 mph (40.2 km/h). For clear openings in excess of 30

to 36 in. (76.2 to 91.4 em) it was shown that grates spaced on 30 in.

(76.2 em) centers would provide satisfactory safety treatment. These find

ings were in fact borne out through six full-scale prototype tests. Tests of

a 30 in. (76.2 em) diameter corrugated steel pipe culvert end, cut to match a

5 to 1 side slope, were successfully conducted. The culvert opening was

readily traversed by both a full-si ze automobil e and a mi ni -s i ze automobil e

at 20 mph (32.2 km/h). Tests of a relatively large box culvert constructed

to match the existing 5 to 1 side slope also verified that grates spaced on

30 in. (76.2 em) centers provide a satisfactory safety treatment. Tests of

this treatment at 20 mph (32.2 km/h) and 60 mph (96.5 km/h) by both full-size

and mi ni -s i ze automobil es were conducted. I twas al so shown that the grates

should be extended and anchored at the flow line to avoid any appreciable

dropoff at the end of the culvert treatment. In one test, vehicle rollover

occurred when the left side wheels dropped off an 18 in. (45.7 em) opening at

the end of the culvert.

Preliminary tests and the prototype tests showed that 3 in. (7.6 em)

I.D. schedule 40 steel pipe grates were of sufficient strength to support a

full-size automobile for simple-supported spans up to approximately 12 ft

(3.7 m). Additional full-scale tests were conducted with a test pit to

determine pipe size requirements for larger spans. Results of these tests

provided the following guidelines:

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Suggested Standard

Schedule 40 Pipe Size

Sean Length (ft) 1.0. (in.)

Up to 12 3.0

12 to 16 3.5

16 through 20 4.0

If midspan vertical supports are used, 3.0 in. (7.62 em) 1.0. standard

schedule 40 pipe can be used for spans up to 20 ft (6.1 m). Other sections

having equivalent strengths could of course be used. Reference may also be

made to an FHWA report (1) for strength requi rements of gr.ates.

Results of the study to evaluate the effect of a ramp at the leading edge

of a culvert opening were inconclusive. HVOSM results indicated that appre

ciablewheel hop could be achieved by a small ramp, thus enabling the vehicle

to clear larger culvert openings. An attempt to verify these findings via a

full-scale test program was made. However, due in part to the test proce

dure, the tests did not provide sufficient data to reach any firm conclu

sions. To minimize damage to test vehicles the area behind the ramp was not

excavated and as a consequence the total wheel drop that would have occurred

otherwise was unobtainable. Further evaluation and testing of ramp treat

ments appear warranted.

Parallel-Drainage Structures

Based on the computer simulations and the preliminary test program it was

shown that the driveway slope should be 6 to 1 or flatter to avoid vehicle

rollover for speeds up to 50 mph (80.5 km/h). The computer simulations indi

cated that the ditch side slope should also be 6 to 1 or flatter. Even at

these relatively flat slopes a vehicle traveling at 50 mph (80.5 km/h) will

become airborne for approximately 65 ft (19.8 m). The computer simulations

H. E. Ros s, et a 1 34

4. Grate members should extend to and be anchored at the flow line. Drop

offs at the end of the culvert should be avoided.

5. Necessary grate member sizes will depend on the span of the grates, the

manner in which the grates are supported and the design vehicle weight.

To support a full-size automobile the following sizes or their equivalent

are adequate.

Suggested Standard

Schedule 40 Pipe Size

S~an Len~th (ft 1 1.0. (i n.l

Up to 12 3.0

12 to 16 3.5

16 through 20 4.0

A 3.0 in. (7.62 cm) 1.0. standard schedule 40 pipe can be used for spans

up to 20 ft (6.1 m) if a midspan vertical support is used.

Parallel-Drainage Structures (for driveways, median crossovers, ramps, etc.)

1. The roadway side slope (or ditch slope) in the vicinity of the driveway

slope should be 6 to 1 or flatter.

2. The driveway slope should be 6 to 1 or flatter.

3. The transition area between the roadway side slope and the driveway slope

shoul d be rounded or smoothed as opposed to an abrupt trans it ion.

4. Safety treatment of the culvert opening should include an end section cut

to match the driveway slope with cross members (grates) spaced approxi

mately every 24 in. (61.0 em) perpendicular to the direction of flow.

5. The cross members should be designed to support a concentrated wheel load

of approximately 10,000 lb (44,480 N) applied at midspan.

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REFERENCES

"Traffic-Safe and Hydraulically Efficient Drainage Practices," National

Cooperative Highway Research Program -- Synthesis of Highway Practice 3,

Highway Research Board, 1969.

Ross, Hayes E., Jr., and Post, E. R •• "Criteria for the Design of Safe

Sloping Culvert Grates," Research Report 140-3, Texas Transportation

Institute, Texas A&M University, August 1971.

3. DeLeys, N. J., "Safety Aspects of Roadside Cross Section Design," Report

No. FHWA-RD-75-41 Federal Highway Administration, February 1975.

4. Ballinger, C. A. and Gade, R. H., "Evaluation- of the Structural Behavior

of Typical Highway Inlet Grates, with Recommended Structural Design Cri

teria," Report No. FHWA-RD-73-90, Federal Highway Administration, Decem

ber 1973.

5. "Improving Safety of Drainage Facil ities," Administrative Circular No.

8-79, Texas State Department of Highways and Public Transportation, Janu

ary 1979.

6. Ross, Hayes E., Jr., Hirsch, T. J., Jackson, Benito, Jr., and Sicking,

Dean, "Safety Treatment of Roadsi de Cross-D rai nage Structures," Research

Report 280-1, Texas Transportation Institute, Texas A&M University, March

1981.

7. Ross, Hayes E., Jr., Hirsch, T. J., Sicking, Dean, "Safety Treatment of

Roadside Parallel-Drainage Structures," Research Report 280-2F, Texas

Transportation Institute, Texas A&M University, June 1981 •

8. "Recommended Procedures for Vehicle Crash Testing of Highway Appurte-

" nances," Transportation Research Circular 191, February 1978.

9. Segal, David J., "Highway-Vehicle-Object-Simulation Model -- 1976," Re

port No. FHWA-RD-76-164, Federal Highway Administration, February 1976.

Documents

Safety Treatment of Roadside Drainage Structures