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Traffic Barrier GuidelinesSection 3.0Potential Roadside ObstaclesHands-On Workshop IIIJuly 2013

111This section discusses the most common roadside fixed objects and slope features that will be encountered when performing a barrier warrant analysis. Potential Roadside Obstacles (cont.)Design Options:Remove obstacle Relocate obstacleReduce impact severityShield obstacleDelineate obstacle

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The Designer shall consider the following design options in the order in which they are listed when analyzing potential obstacles:Remove obstacle always the most desirable, but not always feasible.Relocate obstacle when relocating an obstacle, it shall be placed either in an area that is shielded by otherwise justified barrier or far enough from the roadway so it is unlikely to be struck by an errant vehicle.Reduce impact severity.Shield obstacle.Delineate obstacle. Not used on the Tollway system for items within the Clear Zone

Future maintenance of an obstacle or a barrier shall be considered as part of the evaluation.2Design Process Begins at ConceptRoadside safety MUST be part of the design process from the start.Examples of common issues:Embankment Side SlopesDrainage StructuresDrainageGutterBridge DesignBWA Scope/Work Load Reduced3Experience has shown that if roadside safety and the Barrier Warrant process is considered throughout design, the BWA level of effort will likely be reduced as obstacles will be designed out.3Potential Roadside ObstaclesGutters and CurbsEmbankmentsSign SupportsBridge Piers, Parapets, Abutments & Bridge ConesNoise Abatement WallDrainage StructuresDitchesRiprapRoadway LightingITS SystemsUtility PolesTreesBodies of WaterRock Cuts

4All of these are covered in Section 3.0 in the new manual.4Type G-3 Gutters

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Tollway Standard Drawing B1

All gutter constructed along the Tollway mainline, Collector-Distributor (C-D) roadways, and ramps shall be Type G-3 or G-2 Gutter.

Type G-3 Modified Gutter shall only be used in certain situations.5Type G-2 Gutters

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Tollway Standard Drawing B1

Type G-2 Gutter is used along ramps.

Type G-2 modified gutter is relatively new to the standards and is to be used along ramps in front of Type T1 or Type T1-A Traffic Barrier Terminal --- special situations which we will discuss later with the terminal.6Gutters and Curbs ( Article 3.2)7

Type C Curb

Ramp Toll Plaza OnlyThe construction of gutter and curb along Tollway mainline, plazas and ramps should be considered a method to collect runoff and/or to prevent/minimize erosion of the foreslope and not a method for shielding of roadside obstacles.

Type C Curb detail for placement adjacent to flexible pavement used at Ramp Toll Plazas, parking and maintenance areas.7Gutters and Curbs ( Article 3.2)Gutter may be used with or without guardrail.Guardrail may be used with or without gutter.The need for each is determined independently.Do not use guardrail to shield improperly placed gutter.Guardrail used with gutter shall be at correct offset.8

You can use gutter without guardrail.You can use guardrail without gutter.Or they can be used together, but have to be used correctly.

The need for gutter and the need for guardrail are determined independently.

Guardrail used in conjunction with gutters shall be located such that the offset from the edge of paved shoulder to the face of the guardrail conforms with Standard Drawing C1.8Embankments (Article 3.3)

Roadside Geometry and Terrain Features ,Section 5.2.1 of the AASHTO Guide.9Embankments are the most common encountered obstacle. With limited ROW acquisition the widening projects have created steeper embankment slopes and therefore more slope obstacles to evaluate.

9Embankments (Cont)10Recoverable Foreslope 1:4 (V:H) and flatter

Non-Recoverable Foreslope Between 1:3 (V:H) (inclusive) and 1:4 (V:H) (exclusive)

Critical Foreslope Steeper than 1:3 (V:H)

Recoverable Foreslope slopes which can be safely traversed and upon which a motorist has a reasonable opportunity to regain control of the vehicle.

Non-Recoverable Foreslope slopes which can be safely traversed, but upon which an errant vehicle is unlikely to recover. The run-off-the-road vehicle will likely continue down to the toe of the slope.

Critical Foreslope slope that cannot be safely traversed by a run-off-the-road vehicle. Depending on the encroachment conditions, a vehicle on a critical foreslope may overturn.

10Vehicle on Critical Foreslope

Here is a video of vehicle traveling down a foreslope steeper than 1:3 (V:H)

11Comparative Risk Warrants forEmbankments(RDG Fig. 5-1b)

12When reviewing potential slope obstacles, this Figure should be used for all fill heights.

This Figure shows that critical slopes with a low fill heights do not warrant barrier, but these slopes do not follow Tollway criteria.

The red dot shows that barrier is warranted for a 1:2.5 fill slope when the fill height exceeds approx. 9 ft.12Preferred Typical Section Starting Point

13Barn-roof foreslope using 1:6 allows easier:Placement of signs and light polesTransition to a bridge abutment & bridge cone.Base Sheet M 23

This is the Tollways preferred typical section and should be the starting point for ALL designs13Sign Supports (Article 3.4)Overhead Sign Truss Cantilever TypeOverhead Sign Truss Span Type

14The cantilever sign foundation shown on the left photo, usually cannot be placed far enough from the EOTW because of the arm length.

The span type of truss on the right photo, may require the placement of traffic barriers for shielding. Ideally, this foundation can be placed outside the CZ on the backslope.

Economical overhead sign installations may result in the placement of sign supports and foundations within the clear zone.

Ground mounted sign supports are also included in this article.14Bridge (Article 3.5)

PierAbutment ConeEconomical bridge designs usually result in the location of bridge piers, abutments, and parapets within mainline or ramp clear zones.

Parapets15other typical roadside obstacles are related to bridges. Most contracts have one or more of these bridge obstacles.

New embankment cones and bridge approach roadway embankments generally should be constructed with the same sideslopes as the approach roadway and graded to eliminate the need for traffic barrier along the lower roadway.

Obviously, a bridge pier at the edge of shoulder will require shielding.

The approach end of a bridge rail or parapet also requires shielding to eliminate the blunt end.15Noise Abatement Wall (Article 3.6)Non-Crashworthy Noise WallCrashworthy Noise Wall

16Not preferred for new installationsAnother obstacle that we are seeing more of these days is Noise Abatement Wall. Sometimes just the blunt end where the wall starts is considered as an obstacle. This is the case when the NAW is crash-worthy. Other times the entire wall is also an obstacle that needs to be evaluated.

On a project on the north T/S a Benefit/Cost analysis was performed comparing each of these alternatives and in that case the crash-worthy NAW had a high Benefit/ Cost ratio when compared to the guardrail shielded Non-crashworthy NAW.

Another positive from that analysis is that the Crashworthy NAW eliminated the guardrail.16NAW Preferred InstallationsPlace Wall Near ROW, Beyond Clear Zone

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17NAW Preferred InstallationsWhen along roadway install crashworthy NAW with snow storage (no guardrail for face of wall)18

Base Sheet M2518Drainage Structure Safety End Treatment

Direction of Traffic

Pipe Runners to match adjacent slope19Standards B13 thru B18.

Culverts and drainage structures should be oriented perpendicular to the main flow of traffic with a maximum skew angle of 30 degrees into the direction of traffic, left hand forward, if the culvert opening is located within or near the clear zone and requires pipe runners for the safety end treatment.

The pipe runners have been crash-tested to ensure they are traversable for vehicles. If this orientation cannot be attained a special design is required.

It is important that the pipe runners should be in line with the adjacent slope, providing a smooth transition for an errant vehicle.

It is also important to note that the pipe should be of sufficient length as to not create a steep slope over the pipe or a crater in the slope. Both of these may create a potential obstacle or may be difficult to maintain.19Drainage Structures (Article 3.7)

Issues:Headwall not flush with embankmentPipe too shortHeadwall too close to roadwaySteep slope just above headwallSkew

20Tollway drainage structures are shown on Standards B13 thru 18.

Culverts and drainage structures should be oriented perpendicular to the main flow of traffic, if possible.

Sloped headwalls should be placed perpendicular to the roadway to better fit with the sideslope.

It is also important to note that the pipe should be of sufficient length as to not create a steep slope over the pipe or a crater in the slope. Both of these may create a potential obstacle or may be difficult to maintain.20Drainage Structures- Corrected

21Culvert pipes were lengthened.Sloped headwalls were rotated.Re-grading done.21Drainage Structure- Issues

Issues-Culvert End TreatmentHeadwall & pipe runners too steep in embankment slope, non traversable Headwall not flush with embankment; obstruction

2222Drainage Structure- Corrected

23Slope regradedPipe runners lengthenedRiprap is located outside of clear zone at this location

23Ditches (Article 3.8)

Drainage Channels, Section 3.2.4 of the AASHTO Guide.24Ditch itself is not usually an obstacle.

Tollway standard ditch is 4 flat bottom as shown in RDC 2.6.924Roadway Lighting (Article 3.10)

25Light poles need to be traversable elements.25Standard H1 Grading Requirements

26Standard H1 Grading Requirements

2727Breakaway Light Pole Bases28

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There are five types of breakaway light pole bases commonly found on the Tollway System. However, only two of these types are permitted for use on future design projects.

New projects are permitted to use:

Photo 1: Union Metal frangible base light poles These types of light poles consist of a slip-fitter frangible base which the pole is attached by a rivet. Are easily identified by the presence of this rivet and the lack of a weld along the joint between the pole and the base.

Photo 2: A non-breakaway light pole installed on a 9-inch high breakaway base (sometimes referred to as a 9-inch breakaway transformer base).

Other bases found on the system:

P&K frangible base light poles (Photo 3)

These types of light poles were typically installed prior to 1984 and are similar to the Union Metal frangible base light poles depicted in Photo 1. The main difference between the two is the size of the slip fitter base which is 9 high on the P&K poles.

Slip base light pole (Photo 4)

These types of light poles are no longer manufactured and have been removed from the IDOT Standard Specifications and the Tollway Supplemental Specifications.

Breakaway Couplings (Photo 5)

These types of installations include a non-breakaway light pole installed using breakaway couplings. This type of installation typically indicates that the original light pole was knocked down and replaced by the Tollway Maintenance Division.

Replacement of Old Standard Installations (Photos 3 to 5):

It should be noted that the FHWA does not require replacement of any safety appurtenance with new standards just for the sake of replacing. Installations of safety appurtenances are considered acceptable if they were installed according to the standard at the time of installation. In other words, if the safety appurtenance was crash-worthy at the time of installation, then it is still considered crash-worthy.

Existing installations of the types depicted in Photos 3 to 5 within the limits of future rehabilitation projects may remain in place only if they are unaffected by the work, however, they must be removed and replaced if affected (i.e. relocated). Replacement of these types of installations within the limits of any reconstruction projects should be included as part of the project regardless of the affect on the existing installation.

NOTE: If an installation is encountered within the limits of any type of project within the Tollway System which has two distinct breakaway methods installed at one location, the replacement of such an installation should be recommended by the Designer to the Tollway for inclusion with the project. This shall be regardless of the nature of the work included with the project or if this work affects the light pole.

28Roadway Lighting (Article 3.10)

Controllers and Transformers29Control consoles shall be located such that barrier is not required if at all possible.

If this cannot be done, investigation should be made into locating control consoles behind otherwise-warranted barriers.29Communication Systems and ITS Devices(Article 3.11)

NID RWISCCTV Camera Non-Breakaway30Locate these non-breakaway installations in areas that are inaccessible to errant vehicles or that already require barrier.

CCTV uses coaxial cable which does not breakaway.

CCTV = Closed Circuit Television

RWIS = Roadway Weather Information Station

DSE is responsible for coordinating with Tollway IT Department relative to feasible options / locations for ITS equipment.

NID (Previously identified as RTMS) = Non Intrusive Detection-Traffic Microwave Sensors

RWIS and NID are too heavy to land on the roof of a car.30Bodies of Water (Article 3.14)Bodies of water greater than 2 in depth must be shielded. Locate detention basins well outside the clear zone.

3131Need to consider how often it will have water.

Need to consider normal water vs. high water.

Wet bottom vs. Dry bottom detention basins

Engineering judgment needs to be used.Questions?323232BREAK

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