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.

Validation

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.

Conclusions

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.