The continued growth of HOT (high occupancy toll) lanes beyond very simple initial ones is leading to increased concern about how to enforce occupancy requirements. Most early HOT lanes, with an entrance at one end and an exit at the other, had room to provide an enforcement zone somewhere in between, in which those HOVs which qualified for reduced-rate or zero tolls moved into a separate lane from the other cars paying tolls via transponder. In the “declaration lane,” visual enforcement is the rule—essentially, counting heads by patrol officers, either overhead or alongside. But larger and more complex networks of HOT lanes, especially when retrofitted into existing urban freeways with constrained rights of way, don’t have room for what would have to be numerous declaration lanes. Moreover, the idea of a single location where tolling (and declaration) takes place is also no longer applicable to a network of priced lanes, where people will be charged either by total distance driven (from entry to exit) or for each link in the system that they traverse.

This dilemma surfaced recently in the Seattle area, site of one of FHWA’s Urban Partnership Agreement projects: using electronically collected congestion-priced tolls to manage traffic on, and help finance the replacement of, the SR 520 floating bridge. A study for Washington State DOT by IBI Group, released in January, evaluates five occupancy-enforcement alternatives:

  • Transponders for SOVs plus visual enforcement of HOVs;
  • Transponders for SOVs plus declaration lane for HOVs;
  • Transponders for all plus declaration lane for HOVs;
  • Transponders with declaration feature for all;
  • Transponders for SOVs, license-plate registrations for HOVs.

The fifth of these is what is currently in use on the new I-95 Express Lanes in Miami, the first Urban Partnership project to go into (Phase 1) operation.

The report rejects the first option unreliable, especially on a bridge. And it rejects the second and third due to no room on the bridge for a declaration lane. It rejects the Miami alternative due in part to the potential administrative burden of carpool registration and concern about enforcement. So it recommends going with a more-costly transponder than those currently in use, featuring the addition of a button by which vehicle occupants self-declare how many people are in the vehicle at that time. It claims this would provide “automated enforcement.”

I guess IBI Group and WSDOT have more confidence in people’s honesty than I do. Why would a solo driver running late crossing the bridge be any less likely to divert into the faster HOT-3 lane if he has to press a button claiming there are three people in his car than a similar solo driver who illegally moves into a regular HOV lane? This is not automated enforcement at all. The enforcement is simply the same old unreliable visual enforcement by a patrol officer. If WSDOT is counting on financing several billion dollars worth of SR 520 bridge construction costs via tolling on the honor system, I’d say good luck and good-bye if I were a potential investor.

An alternative to this honor system approach is what I recommended to Florida DOT for the I-95 Express project: registered carpools with transponders recognized by the toll system’s software as qualifying for a special rate during peak periods and the regular rate at all other times. Occupancy enforcement would be the responsibility of the ride-sharing agency that does the registration, which would work with participating employers to audit the system on a regular basis to verify that those claiming to be commuter carpools are still, in fact, in operation. Under this approach, all enforcement would be electronic toll enforcement: Is there a functioning transponder, what toll rate applies at this time of day, and what is the status of the customer’s account?

FDOT accepted the registered carpool idea, but not the transponder enforcement approach, preferring to go with a decal on each registered vehicle plus the license plate number entered into the system software. Hence, actual enforcement still requires a state trooper to be there and count heads.

I fleshed out this idea in a paper and poster session for the 2009 Transportation Research Board annual meeting. It’s paper #09-0385 (“Automating Managed Lanes Enforcement”) on the 2009 Annual Meeting CD-ROM, if you attended and have one. If you don’t have the CD and would like a copy of the paper, just send me an email request and I’ll send it to you.