The Michigan Department of Transportation estimated that an ITS-based active overheight detection and warning system installed at both approaches to a bridge would cost $110,000.
Overheight trucks traveling on I-96 in Oakland County, Michigan, between the Livingston County line and I-275, have had a history of collisions resulting in damage to structures with sub-standard vertical clearance. As a result, the Michigan Department of Transportation (MDOT) conducted a study to examine strategies to mitigate these bridge-hit incidents and corollary damage costs. The locations studied were: bridges for Beck Road, Wixom Road and Old Plank Road over I-96, all of which have less than 15 feet clearance whereas the Michigan State under clearance requirement is 16 feet. The study analyzed the current state of practice as well as the average costs of various overheight warning/detection alternatives – traditional as well as ITS technology-based solutions.
A survey of nine state departments of transportation (DOT) was conducted to assess potential options available to MDOT. Also, an Internet based literature search was conducted to find the relevant literature from the Web sites of the Transportation Research Information Services (TRIS) Database, ITS America (ITSA), and the Institute of Transportation Engineers (ITE).
Of the nine surveys sent to the state DOTs, five were returned. The agencies that responded were:
- Arizona Department of Transportation
- Iowa Department of Transportation
- Mississippi Department of Transportation
- Oregon Department of Transportation
- North Carolina Department of Transportation
Two of the responding agencies, Mississippi and North Carolina, had long-term (over 10 years) use and experience with overheight vehicle detection systems. Iowa had recently installed the system, and had a favorable opinion during the short operational period. Arizona DOT which utilizes this technology, currently does not have any permanent installations as some installed systems were removed after the structure height was raised, but does utilize overheight detection when the construction work requires lowering under clearance of the structures.
Two state DOTs provided feedback, but did not respond to the survey. Illinois DOT disclosed that they no longer used the overheight vehicle detection technology although they had in the past. Wisconsin DOT reported they decided against installing overheight detection technology, on a recently bid project, because of the cost.
The MDOT examined three alternatives for overheight vehicle warning systems, which included traditional as well as technology based solutions, and estimated the cost of each. The cost estimates were based on the data provided by manufacturers, supplemented by the information received from the state DOTs that responded to the MDOT survey. Table 1 shows the estimated installed cost for each alternative. Installation at two sites is assumed, one for each approach to the bridge.
Table 1 – Cost Comparisons for Overheight Warning Action Alternatives
Passive Signing and Permitting
Requires increased permit awareness
Can create liability for agency
Active Detection and Warning System
Will not eliminate all collisions
Passing Signing and Permitting. This alternative consists of signing and continued permit process (possibly with increased promotion outreach to increase awareness). Average cost is $9,000. The alternative is estimated to be 10-20 percent effective in eliminating incidents.
Sacrificial Structure or Chains/Metal Strips. This alternative uses physical notification or a sacrificial structure. This would consist of chains/metal foil strips hanging as a target in advance of the bridge structure or possibly a false structure to warn drivers their vehicles are overheight. Average cost is $62,000. The alternative is estimated to be 30-50 percent effective.
Active Detection and Warning System. This is an ITS-based active warning alternative, which utilizes electronics to detect the overheight vehicle and provides a visible/audible warning. The system consists of an infrared transmitter, receiver, and a warning sign with alternating flashers and optional audible alarms. The infrared beam when broken triggers an electronic response to activate the flashers as well as the audible alarm. Average cost is $110,000. This active warning system is estimated to be 50-80 percent effective.
The analysis shows that an ITS based active overheight detection and warning system installed at both approaches to a bridge would cost $110,000, which is substantially higher than the cost of a non-ITS based solution, but would be more effective in reducing the bridge-hit incidents.
Evaluation of Overheight Vehicle Detection/Warning Systems
Author: Cawley, Patrick M., PE, PTOE
Published By: Paper presented at the 2002 ITE Spring Conference and Exhibit, Palm Harbor, Florida
Source Date: 24-27 March 2002
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