The Los Angeles County MTA helps facilitate ridesharing both for commuters and students.

At many companies today, employees get help with the commute. “Ridematching” databases match employees into vanpools. Commute challenges offer prizes for environmentally friendly commuters. Transit passes can be purchased with pretax salary, as an employee benefit. These ridesharing, information, and incentive programs fall under the term “travel demand management,” or TDM. (It’s a topic dear to TransitCenter’s heart because we got our start providing those transit passes to employers.)

TDM, which is often supported with government transportation funding (and mandated in some parts of the country) is widely viewed as a cost-effective way to reduce driving and cut congestion. In fact, a Federal Highway Administration desk reference asserts that “Nothing is more cost-effective than TDM.” But this blanket statement glosses over a wide range of outcomes.

Cambridge Systematics estimates that a comprehensive TDM package of information, alternative commute offerings like rideshare, and financial incentives can cut drive-alone trips by 15-20% at a site with access to rail – and 25-30% if parking isn’t free. But move to a transit desert with free parking and poor bus service, and that same TDM package will only convince 3-7% of people to switch to another mode.

This might be because in places that are dense and walkable enough to support a good transit system, there’s a significant pool of potential customers for sustainable transportation. Transit (or another sustainable mode) is fast, reliable, and convenient enough for commuters, but something besides travel time or service quality holds them back. They might not realize there’s a bus stop near their workplace. They might feel the train is too costly. They might be too worried about a home emergency to rely on a carpool, or too worried about theft to ride their bike. For whatever reason, they’re a step away from choosing sustainable transportation.

TDM can get them to take that step. The result: Significant mode shift due to  modest investments like information for the bus rider, a subsidized monthly pass for the train commuter, a “guaranteed ride home” for the carpooler, and secure bike parking at the office.

Meanwhile, in sprawling places, where transit (and other sustainable modes) are not fast or convenient enough for most people’s commutes, no information packet or vanpool can change that. In a transit desert, the pool of potential customers is more like a puddle.

If that’s the case, TDM may be a critical complement to transit – but it’s no substitute. So it was heartening to see the TDM professionals at Mobility Lab in Arlington, Virginia slam Apple for building its new headquarters in an isolated freeway location. Apple announced it would spend $35 million on TDM, so you might think folks in the TDM business would be ready with a standing ovation. Instead, Mobility Lab’s Tom Fairchild said Apple was stuck in the past, writing that “even the best [TDM] program cannot make up for a disastrous location.”

There’s another big wrinkle when it comes to the perception of TDM as cost-effective. While measuring the impact of a particular TDM project can be fairly straightforward, seeing the big picture — the regional impact – is not. FHWA admits that “A standardized methodology for evaluating TDM strategies does not yet exist in the U.S.” Instead, we get comparative results that really aren’t comparable:

South Florida’s TDM agency credited its work with reducing driving by 57.6 million miles a year – nothing to sneeze at. Phoenix, though, claimed results that were 57 times as high (and four times as high as was reported in Washington). Is it possible that there’s really such wide variance in impacts? Or is it more likely that these places include different activities in their definitions of TDM and use different methodologies to measure the impact of TDM activities?

TDM has a lot to recommend it. It creates partnerships between government and employers and other institutions. It counterbalances the incentives to drive that are built into subsidies of parking and roads. And it may be a powerful way to build transit ridership in some areas. It’s also an area that deserves a lot more study.