Includes highway safety publications and journals on road maintenance, engineering and injury litigation, as well as traffic safety facts, accident and collision investigation information and consulting, court and liability issues, and links to transportation related organizations such as departments of transportation and safety organizations.  Also includes discussion of road construction issues, legal cases on traffic accidents and collisions, and other information on highway safety.  See our highway safety expert services and publications.
Road Management & Engineering Journal
Copyright © 1997 by TranSafety, Inc.
March 1, 1997
TranSafety, Inc.
(360) 683-6276
Fax: (360) 335-6402

Addressing Human Factors and Injury Accidents Through the Safety Management System
Winter Maintenance Technology Practices -- Learning from Abroad
Township Must Erect and Maintain Stop Signs Where Township Road Intersects State Road
Inventorying Highway Signs
Call Boxes in Freeway Medians?

Inventorying Highway Signs

The State of Connecticut s Department of Transportation (ConnDOT) is adapting the videodisc-based system used to photolog its 3,900 miles of highway to the task of inventorying its road signs and supports. ConnDOT personnel designed the resulting Videodisc-based Sign Inventory System (VSIS) to meet three pressing needs:

  • To protect Connecticut s investment in about 170,000 highway signs valued at more than $50 million. Updating the present fragmented record with special-purpose field trips would be prohibitively expensive and poses safety problems for field crews. ConnDOT needs a flexible, cost-effective, user-friendly system that can be piggybacked onto existing highway inventory systems and can interface with all segments of its computerized record keeping system to maintain a current, easily accessed inventory.

  • To reduce the growing number of civil lawsuits against the state alleging defective highway signage. According to one study, defective signs figure in 20 percent of tort liability actions and are cited as a main cause in 41 percent of serious crashes.

  • To meet potential mandates for an integrated highway safety management system proposed by the federal Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991.

In a paper entitled Development of the Connecticut Department of Transportation s Videodisc-based Sign Inventory System (VSIS) and presented at the 74th Annual Meeting of the Transportation Research Board (January 1995), Richard C. Hanley described the progress of the new system.

Adapting the Photolog

ConnDOT s photolog is a set of photographic images on videodisc. Moving vehicles gather these images of the state-maintained highway system by taking a photograph every 0.01 miles. The resulting videodisc becomes a continuously running representation of the roadway showing, among other things, the signs and supports along the side of the road.

ConnDOT encountered three problems in adapting the existing photolog system to an inventory of signage:

  • Poor image resolution. Some loss of sharpness and sign legibility resulted when transferring images from film to videodisc. To solve this problem, ConnDOT personnel also transferred close-up images of roadside areas with high sign density. Studies during the proposal phase of the project showed that close- ups combined with the photolog s normal, wide-angle scans would help improve sign legibility. Initial figures indicated sign legibility in these sign-zoom scans increased from 55 to almost 95 percent.

  • Mismatched mileage readings. ConnDOT originally established standard roadway mileage readings using a vehicle-mounted fifth-wheel device to record mileages. The mileage readings on photolog vehicles have never exactly matched standard highway mileages. A proposed solution is to use database videolinks to link videodisc and official highway log mileages. Photolog vehicles would establish these videolinks each year to reconcile the standard mileages with photolog mileages for highway signs.

  • Ramps. Sign inventories need to include signs on access ramps; however, photolog surveys have never filmed access ramps. A partial solution would be to integrate real world measurements of exact sign size and position with long-range scans of the on-off ramp signs taken from the main highway. The Federal Highway Administration had used a similar system to take measurements for installing signs, but that software proved incompatible with ConnDOT s database software. Hanley mentioned that efforts to develop a system of sign location and dimensioning would be part of ongoing future research.

A longer term solution would be to include access ramps in photolog surveys. ConnDOT had developed a proposal to implement this complex operation.

Adapting the Database

The second phase of the videodisc-based sign inventory project was developing a user-friendly system for accessing and integrating the many databases in the ConnDOT system. ConnDOT chose an open network of powerful personal computers rather than a mainframe interface to eliminate the need for trained operators and avoid the resulting bottleneck.

After reviewing various database products, ConnDOT selected the Foxpro database programming language, which permits the integration of database and videodisc information. The program supports Structure Query Language (SQL) and Open Database Connectivity (ODBC) standards, both essential to future operations of the open system.

Features of this mouse-based, point-and-click system allow personnel throughout ConnDOT to scan specific routes and check the position and size of specific signs. ConnDOT employees can use the computer system to check for errors in and update the data banks, correlate information from multiple sites, access catalogs and standards, initiate queries, and indicate needed changes in the signage.


In the third phase of the project, ConnDOT used both field crews and the Videodisc-based Sign Inventory System to perform a sign inventory on three sample routes. Project researchers then analyzed the data obtained through both methods and made cost, labor, and time comparisons. The unspecified percentage of discrepancies between the two surveys resulted mainly from the difficulty of photologging signs on access ramps.

The sign-zoom images proved less useful on limited-access highways than expected, due in part to the fact that most signs were easy to interpret from the photolog s normal-view images. In addition, overhead-mounted signs were generally large and easily read, while left-mounted signs were few and usually standard in design (e.g., no-passing flags). Finally, close-up images did not make it possible to see through line-of-sight obstructions such as foliage and parked vehicles. Sign legibility with the VSIS ranged from 86 to 93 percent.

The biggest savings of the photolog system was in time. Since photolog surveys must be done in any case, photologs are always available at any terminal. Even with supplementary field trips, Hanley estimated that the VSIS was five times as fast as field-trip-only surveys, and VSIS surveys would require only 40 percent of the mileage.


Hanley estimated that a completed VSIS would yield initial savings of 60,000 miles of travel, 40,000 person-hours, and more than $800,000 over a statewide field inventory of highway signs. These savings would be in addition to a reduction of hazard to survey crews.

Proposed refinements included incorporation of more capable hardware and software, establishment of tighter communications (especially the videolinks mentioned above) among components of the system, and staffing changes to maintain the system. Hanley also recommended that photolog surveys include access ramps and that the number of frames taken during photologging be increased from 100 to 200 per mile. Hanley felt this could improve sign legibility by 10 percent. He recommended against the use of sign-zoom images for now.

Copyright © 1997 by TranSafety, Inc.

Back to the Road Management Journal Index