Tuesday, June 28, 2016

Remember: changing road pricing can have unintended consequences

A few years ago, I wrote about how the 1996 changing of the toll structure of the Turnpike in Newton dramatically affected traffic. In that case, changing the toll by $1 created a new calculus where many commuters took an alternate route to avoid the toll, leading to traffic on side roads. The state will soon change the toll structure on the Tobin Bridge, going from $2.50 in one direction to $1.25 in each way. They claim it will be revenue neutral (it will likely be somewhat revenue positive, actually; see below), but there is not talk of the traffic impact, because the amount you're charging is the same, so it won't change the traffic, right?

Wrong. There may be a major traffic impact.

First, the revenue projections. It is very likely that revenue will actually go up. Today, it costs $2.50 to go south on the Tobin, and it is free going north. For a motorist coming south on 95 in Peabody, it is usually only 2 to 3 minutes longer to loop around on 128 and 93 versus the trip straight down Route 1. (At rush hour, it depends more on traffic, but the majority of travel on the Tobin Bridge is at non-rush times.) The 128-93 route is about five miles further, but even assuming 50¢ for gas (most motorists don't figure in the full marginal cost of a mile traveled, many probably discount the extra gas anyway) it is still a saving of $2 for three minutes of time, a rate of $40 per hour. That's generally worth it.

Which is much of the reason why, in 2015, there were 51,000 northbound vehicles daily on the Tobin, but just 34,000 going southbound. (Some of this may be explained by things like the location of on- and off-ramps and traffic patterns, but most of it is likely due to the toll.)

Equalizing the toll will change this calculus dramatically. Many motorists who had balked at the $2.50 toll may be more willing to part with $1.25 to save a couple of minutes. And while some will avoid the bridge northbound, it will be far fewer than if the toll were flipped and it was charged full rate northbound, and free coming south. Guessing wildly, I'd guess that 5,000 motorists will use the bridge coming south, and 5,000 will abandon it going north. This means a lot of new toll revenue for the state.

Currently, the state collects $2.50 from each of the vehicles using the bridge southbound (we'll assume that the higher rate for larger vehicles offsets the discounted toll charged to Charlestown and Chelsea residents). With 34,215 vehicles counted per weekday in 2015, this amounts to $85,537.50 in toll revenue. My wild-guess assumption is that there will be 5,000 more southbound travelers (39,215) and 5,000 fewer northbound travelers (46,108), each paying $1.25, for a total of $106,653.75, or an additional $20,000 in toll revenue daily. Even discounting lower traffic on weekends and holidays, this will probably add in the neighborhood of five to six million additional dollars of toll revenue for the state.

The tolls will be fairer and make more sense and raises more money for the state, which can always use more money for infrastructure. This is a win-win …

… unless it has an unforeseen impact traffic. The bridge itself is nowhere near congested, especially coming southbound, where peak-hour traffic counts average just 3000 per hour (1000 per lane per hour), well below the 1500 where congestion begins in earnest (in the chart above, you can see how the northbound traffic levels off at about 4000 per hour, even dipping slightly during the 4 to 5 p.m. peak, which may be due to heavy traffic on roadways accessing the bridge reducing throughput). The issue with more inbound traffic is at the end of the bridge.

Most of the traffic (about 85%) stays on the loop ramp to the Leverett Connector and O'Neill Tunnel. An additional stream of traffic is added from Rutherford Avenue, and there is considerable merging and sorting of this traffic. With only two lanes, this is much nearer capacity; adding more vehicles may create merge traffic which will cause significant backups. The traffic on the Leverett Connector and the tunnel should be a zero-sum game, shifting users from I-93 to Route 1, much like the Turnpike toll removal didn't necessarily increase traffic, but changed where it got on and off of the highway. Even minor changes can have consequences. This one may work fine. Or it may not.

Still, I'm for this change, as it is sensible policy (even if it might have some unintended consequences). In fact, the Commonwealth should explore avenues to toll all the highways leading in to Boston at a rate equal to the Turnpike. Tolls on the Turnpike are not a detriment to the local economy, which seems fine to be churning alone just fine. And other than federal policy (which may be changing), there is no logical reason why Turnpike commuters should have to pay $5 a day to get from 128 to the city while I-93 commuters get in for free. And while the dollars from the Tobin change are relatively small, charging a sort-of congestion charge for other highways leading in to Boston could bring in big dollars. I-93 could be tolled at $2.50 in both directions from 128 to the city, with a lower toll for Route 2 ($1.25), perhaps waived for commuters parking at Alewife. The harbor tunnel tolls, currently $3.50 one way, could be reduced to $1.25 each way to match the other tolls.

At this rate, and assuming that 10% of travelers would carpool, take transit or use side roads to avoid the tolls (although with electronic tolling, it's harder to simply avoid a toll booth), this would increase the equity of the transportation system, while at the same time raising more than $600 million annually for road maintenance. Considering the age and state of many of the roadways, bridges and tunnels in the Commonwealth, this money could be spent making sure that the roadways are maintained statewide. Unlike a vehicle mile tax, this is not a new concept; it's one which has been in place on roadways throughout the Commonwealth for nearly a century (far longer if you account for the 19th century incarnations). And unlike a statewide gas tax, this targets users of the state's most crowded and overtaxed infrastructure, and may be a factor leading drivers to consider other modes, which often run parallel. The Turnpike users already pay tolls. It's high time others did a well.


  1. The Tobin bridge is rarely congested because there are big bottlenecks on either end. On the south, it's fed by the Central Artery, which is already pretty jammed throughout rush hour, and on the north end it connects to the surface Route 1, which results in pretty large queues during PM rush hours. In fact, having a northbound toll on the bridge might make these queues somewhat smaller and would thus improve operations on the 426 and 428 buses.

    1. The point is less that tolling northbound may decrease traffic (it probably will) but that reducing the toll southbound will likely increase traffic, pushing more traffic in to the already-over-capacity artery. The congestion likely won't be because of the bridge itself, but because of what it feeds in to.

  2. I think you have northbound and southbound switched in the sixth paragraph?