Following the Implementation of an Overheight Vehicle Detection System, No Bridge Strikes Were Reported at the Historically Problematic Low-Clearance Overpass in Maine.

Researchers Investigated the Effectiveness of Seven Dynamic Message Signs, Variable Speed Limit Signs, and an Overheight Vehicle Detection System system in Maine.

Date Posted

Maine Statewide Deployment and Integration of Advanced Traveler Information Systems

Summary Information

Active Traveler Information Systems (AITS) such as dynamic message signs (DMS), variable speed limit signs (VSLS), and overheight vehicle detection (OHVD) systems are valuable tools for the communication of important information to the traveling public. This study investigated the effectiveness of seven DMS locations along I-95 and I-295, VSLS along the Maine Interstate and Maine Turnpike corridors, and an OHVD system deployed on a suburban arterial roughly 500ft prior to passing underneath I-95 in Bangor, Maine. Designed to identify overheight vehicles approaching overhead structures, the OHVD system operates in two stages: initially, warning lights alert the driver about potential height clearance issues with structures such as bridges, overpasses, and tunnels. If the vehicle persists, cameras are activated which capture an image of the vehicle's license plate and record the subsequent five minutes of footage. 


The DMS in Maine displays a variety of information, including weather and roadway conditions, special events, travel times, enforcement actions, and congestion management. For the VSLS system, speeds were collected in 2-hour intervals during the morning or evening commute (with a radar gun) during numerous inclement weather events throughout the 2006–2008 winter season. User satisfaction for the DMS and VSLS system was collected through a survey that received 62 responses. Two OHVD systems were installed at an initial cost of $173,000 in August 2006 in response to multiple overpass strikes—15 over the past 12 years, three of which required repairs exceeding $60,000. The study compared eastbound bridge strike data before and after the deployment of the OHVD system in Bangor, Maine, on US-2, where it passes under I-95. To assess system' impact, data from 2006 to 2009 were compared against data from 1994 to 2006. 



  • Among the participants who encountered messages on the DMS along sections of the Maine Interstate (98 percent), 72 percent found the displayed information useful. However, only 31 percent of these participants used this information to modify their originally planned travel route.
  • Additionally, 64 percent of participants would find it useful if the DMS displayed air or roadway temperature during the winter.


  • While 56 percent of survey respondents found the VSLS beneficial during winter driving and nearly half of them (45 percent) reported adjusting their speed to match VSLS displays, actual speed data showed minimal, if any, impact on driving speeds.
  • A significant 85 percent of participants noticed active VSLS even under dry, non-precipitating conditions.
  • The likelihood of adherence to the advisory might increase if road conditions or reasons for speed limit reductions were displayed on a DMS, as suggested by participants.


  • The study findings suggest a probable connection between the implementation of the OHVD and the observed reduction in bridge strikes to zero (during 2006-2009). However, there is a 15 percent probability that this reduction could have occurred in the absence of the OHVD. During the three-year period under consideration, a bridge strike was reported in the westbound direction, an area where the OHVD was not deployed.
Goal Areas
Results Type
Deployment Locations