Speed Reduction Strategies

Ali Kamyab, Research ScientistTom Maze, ProfessorCTRE, Iowa State University

Started in 1999 to research, test and evaluate work zone safety technologyOriginally the states of Iowa, Kansas, Missouri, and Nebraska

2001 Wisconsin joinedExpecting Minnesota and Georgia to become members soon

Iowa’s programFocused on rural work zones and on speed reductionInitially focused on testing technology to moderate speeds (tactical level)Next provided a broader look at strategies (strategic level)

Policy actionsTechnology applicationsRegulatory/enforcement strategies

Currently exploring design, traffic management, planning, and enforcement issues

2000 synthesis of speed reduction strategies

Regulatory and advisory speed limit signsLane width reductionFlaggersPolice enforcementDrone radarSpeed display monitoringRumble stripsOptical speed bars

Report’s main conclusion

“None of the techniques individually are capable of reducing vehicle speeds to the desired level. Effective speed reductions will probably involve some combination of technologies and policies.”

Regulatory and advisory signs

Advisory signs – little impactIncreased frequency of signs – no impactRegulatory – impact when enforcedRegulatory signs with strobes – some impact

Lane width reductionIt matter how the lane width reduction is done

Cones – little impactConcrete barriers – more impact

Lane width reduction – reduce speed by 0 – 16%*Lane width reduction – may have minimal impact**

*Richards, S.H., R.C.Wunderlich, and C.L. Dudek, “Controlling Speeds in Highway Work Zones, TTI, 1984**Benekohal, R.F., Kastel, L.M., and M. Suhale, “Evaluation of Work Zone Speed Control Techniques, TRR 1035, 1985

Flagging Significant impact*

Improves with training of flagger7-13 mph on rural interstates10 – 16 mph on two lane roads13 mph on urban arterial streets

Labor intensiveFatiguing

* Richards, S.H., R.C.Wunderlich, and C.L. Dudek, “Controlling Speeds in Highway Work Zones, TTI, 1984

EnforcementSignificant impactStationary squad car – reduce 6 to 22 percent*Circulating patrol car – 3 to 5 percent speed reduction*

* Richards, S.H., Wunderlich, R.C., and C.L. Dudek, “Field Evaluation of Work Zone Speed Control Techniques, TRR 1035, 1985

Drone radar, Speed monitor display, and Rumble strips

Drone radarMinimal impact

Speed monitor displaysImpact significant at the beginning Impact tends to wane with time

Rumble stripsReduction of average speed by few mph

Optical speed barsReduce the 85th percentile speed and the mean speedSignificant reduction of the standard deviation of speed

Source Meyer, E., “A New Look at Optical Speed Bars,” ITE Journal November, 2001

Conclusions

All technology provides some benefitsThe impact of all technology diminishes with timeEnforcement’s impact is consistent with time

Reduction continues for a short period even after enforcement leaves

Results of state DOT survey (36 agency responses)

Applicable

No Yes Effective Ineffective

Partially Effective

No Information

Regulatory signs 6 28 2 7 10 9 Advisory signs 26 8 2 0 3 3 CMS 16 18 4 2 5 7 Police enforcement 8 26 18 0 5 3 Ghost police car 32 2 1 0 1 0 Flaggers 32 2 2 0 0 0 Speed display 28 6 2 1 2 1 Drone radar 28 6 2 1 2 1 Rumble strips 33 1 0 0 1 0 Lane narrowing 31 3 2 0 0 1 Pavement markings 33 1 0 0 0 1 HAR 32 2 0 0 1 1

Results of second state DOT survey

28 state responses

Results of stepped up enforcement experiment

Iowa’s Evaluation of the Wizard CB Alert System

Why Rural Focus?Increased frequency of constructionIncreased congestionAggressiveness of drivers

Motivation for Iowa DOT Concern

Safety (worker and motorist)Rural congestionEfficiency of operations

Wizard CB Alert SystemDesigned and patented by Highway Technologies, Inc.Built and marketed by TRAFCON Industries, Inc.Developed at the request of the Pennsylvania Department of Transportation

CB warning for upcoming delaysFocuses on trucks – most common users of CBs• Typically heavy trucks represent 30% or

more of the traffic• Attempts to moderate speed before

reaching work zones

Evaluation case studyMoving work zone

• I-35 paint stripping crew• Warning on channel 19

Work zone characteristics• Moving at 25 mph• Four to five vehicles spread

over about one-mile• Lead vehicle is stripping

truck• Trailing pick-up with

flashing board“CENTERLINE/EDGELINE

PAINT AHEAD”

Wizard CB alert system experiment

Broadcast at 30-second intervalBroadcast on channel 19 (only one channel)Varied message depending on user response

Evaluation questions1. Did truck operators actually receive the

message?2. Did the message effectively alert the

drivers?

Data collection challengesMoving work zone – making speed measurement difficultNo means to stop truck operators to question them

Two proxy measures of effectiveness

Questionnaire administered to truck operators upstream at rest areaMonitor CB channel for truck operator comments (in tailing vehicle)

Modifying warning 1. This is the Iowa DOT. Slow-moving paint

operation in the right lane of north bound Interstate 35. Please use caution.

2. This is the Iowa DOT. Slow-moving paint operation in the right lane of northbound Interstate 35 – milepost 160 to milepost 170. Please use caution.

Modifications continued3. This is the Iowa DOT. Northbound drivers

on Interstate 35, you are approaching a slow-moving paint crew in the right lane. Please use caution.

4. This is an Iowa DOT road work alert. Northbound drivers on Interstate 35, you are approaching a slow-moving paint crew in the right lane. Please use caution.

Evaluation resultsCB Radio Comments• Operators expressed their disapproval

over the work zone itself• Many noticed the new and different

message – majority were positive.“That’s the first time I’ve ever heard anything

like that. I wish everyone would do that. It’d make things a lot easier”

“Get off my radio. You need to get a regular radio station and warn those four wheelers.”

Rest Area Survey1. How years of profession driving do you

have?2. Do you have a CB?3. Did you see the paint crew and, if so,

what was your first alert?4. Did you hear the CB alert?5. Did you think the alert was effective?6. Was the message annoying?

Rest area results

94 total interviews88 (94%) had CBsOf those with CBs, 70 were tuned to channel 19 (80%)59 of those with CB tuned to channel 19 passed the paint crew (63%)

What alerted you first?CB Alert Message 24 (40%)Lights on Trucks 14 (24%)Signs 10 (17%)Arrow Board 7 (12%)Other Truck Drivers 4 (7%)

Total 59 (100%)

Out of the 59, 44 said they heard the CB message (75%)Out of the 44, 39 (89%) thought it was effective Out of 44, 1 said the message was annoying

Example Comments“This could save accidents from happening”“This alerts everybody. It’s a good idea.”“Neat idea! More states should use this!”“A good idea, but sooner (warning) would be more helpful.”

Conclusions

No hard data was available• System appears to be effective

– 41% stated CB alert was their first warning– Generally popular with truck operators

How the warning is phrased is important

Acknowledgements

This work was sponsored through Midwest States Smart Work Zone

Deployment Initiative and sponsored by the Iowa Department

of Transportation

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