Induced demand and transit

Jarrett, as he usually does, has another interesting post up on Human Transit on the subject of whether or not rail attracts more riders than bus.  He points to some research done by a Munich transit planner (who subsequently joins the conversation in the comments) suggesting that this is the case, comparing various mid-sized (under 500,000) European cities with trams and without, noting that the cities considered in the study who have trams generally have higher ridership than those without.

Jarrett asked the fundamental chicken-and-egg question:  Was the construction of streetcars (in most cases, lines running in an exclusive right-of-way, functionally more similar to the MAX Yellow Line than Portland Streetcar) a driver of demand, or a response to it?  In other words, "did the trams cause the ridership, or did the ridership cause the tram?"

The chicken...

This is a good question.  A big technical advantage of rail over bus is vastly greater passenger capacity--and many successful rail lines have been built in bus corridors that got too crowded.  A common argument against rail projects (or against capital-intensive busways) in corridors that aren't already crushloaded to the gills at three minute headways, is "the existing demand doesn't justify the investment".   One commentor, "Danny", asserted that:

All successful high speed rail systems were capacity expansions for crowded low speed rail systems. All failing systems were constructed under the impression that speed causes ridership. 

While I respectfully disagree with his use of the universal quantifier "all"; and I  disagree with the first half of his statement completely (I can think of many counter-examples), the second half of the sentence has a lot of truth:  Many "failing" systems (by which I assume he means systems with usage levels far less than predicted) were constructed based on ridership increases which didn't come too pass.  If you build a rapid transit line in place of a local bus line and cancel (or reduce in frequency) the latter, you already have established a reasonable floor for the utilization of the rapid transit line--the bulk of the bus passengers will switch.  OTOH, if you are anticipating additional ridership that isn't there... there's a far greater chance you will be wrong.

...or the egg?

But, there's also a good chance you'll be right.  The Munich transit planner who produced the above-referenced paper surfaced in the comments, and had this to say. 

When you have cities of a similar size and density usually you should expect a similar ridership of public transit. But obviously, in average, it is not like that. So I sent Jarrett the data as one indicator for this "tram bonus", as we call it, that is able to get people out of their cars, like a bus system would never be able to do it.

Even the successful BRT systems in different cities do usually just channel a demand that already exist, a high demand of captive riders. Who ever has a car in those cities still uses it. 

We believe in the ability of a tram system to attract more people, people who would never set a foot into a bus, and we invest a lot of money in that. And: no matter if we are right or wrong with this "belief", it does work indeed. We see the numbers, we see the ticket sales and it makes sense, even from the economic perspective. It does not make sense for any bus line, but you can expect to increase ridership in a dimension of 50% to 100% on a line, compared to the bus service. If that makes sense for you, then do it.

Doug Allen, a local transit advocate (who was involved in the planning for the initial MAX line, and still works for TriMet--his words, obviously, aren't necessarily the opinions of his employer) added his two cents:

I would agree with "TransitPlannerMunich" that experience with the conversion of a bus route to tram, in a city with a mature system of bus and rail, can provide insight into whether passengers prefer rail over bus.

The implementation of the "Yellow" light rail line in Portland Oregon also showed that a rail line that is shorter and less frequent than the bus service that it replaced can attract higher ridership, no matter how irrational this may seem.

Doug refers to the now-gone 5/Interstate, which ran from Hayden Island along Interstate Avenue to downtown Portland.  The Yellow Line doesn't presently serve the island, and runs at 15 minute headways, so in at least two respects, it's inferior to the bus service it replaced.

Neither Doug or "TransitPlannerMunich" offered any explanation why they observe a presence for rail; formal research on the "tram bonus" is inconclusive.  And other commenters wondered whether or not reconfigurations of bus service (converting parallel downtown routes into feeder routes) might boost rail ridership without boosting overall commute share.  Many properties which riders attribute to bus and rail, are often properties of the local implementation thereof--if, for example a transit agency operates 40' diesel busses through rough neighborhoods with no capital improvements on the bus routes, alongside modern light rail that sticks to the nicer parts of town--don't be surprised if local residents characterize the bus as dirty, noisy, slow, unreliable, and full of unsavory characters.  Bus can be clean and fast, and rail can be slow and uncomfortable; there is much overlap in the service parameters for both.   On the other hand, if there is a demonstrated community preference for one mode over the other--even if entirely irrational--that's something that ought to be factored into planning.

Induced demand

Which leads us to the subject of induced demand-- the "Field of Dreams" problem. ("If you build it, they will come").  If the supply of a given resource is increased, then more of it is often consumed.  This is especially true when the existing supply is insufficient (or barely sufficient) to meet the existing demand; there's often lots of pent-up demand that is more than happy to consume the new supply.  A related phenomenon is value-induced demand; if you increase the value (quality) of a resource, without increasing the cost, demand will also rise.  Both phenomena are in the realm of Economics 101.

Induced demand is frequently invoked in arguments concerning construction or expansion of freeways, where congestion relief is cited as a justification for the bulldozer and the mixer.  Highway opponents frequently point out that when freeway capacity is added, it frequently fills up with additional traffic, causing a failure to deliver on the expected congestion relief.  (Freeways suffer from a fundamental scalibility problem as well--additional traffic, even if below capacity, increases the chance of a wreck, stall, or other incident which severely impacts service.) 

But induced demand works for transit as well.  Transit opponents frequently point out the same thing about transit projects sold on the basis of congestion relief--even if the transit service attracts motorists out of their cars, other motorists often take their place.  But the principle applies:  When transit service improves, either in capacity or in quality, more people will elect to use it.  The improvement can be manifested in values which are easily measured--coverage, capacity, frequency, speed, reliability--or in those values which are less tangible and may reflect social facts or personal biases (comfort, prestige, sex appeal, environmental benefits, etc).  Either way, if you make a service more attractive to the population, more people will use it.  And the advantage that transit has over the automobile (considering only the geometric aspects of it, and ignoring the numerous negative externalities of cars which provide ample additional reasons for transit construction) is one of scalability at high density.
 
The reverse phenomenon is also readily observed:  when you cut service, ridership levels go down--decreases in line frequency or other service parameters will often drive riders to other modes, or to not make trips at all.

How badly do you want it?

These phenomena can be explained by the property of elasticity--a concept which is the way economists answer the question, "how badly do you want it?".  (Actually, it measures the inverse of that question--a lower elasticity means that the product or service is "wanted more badly").  Many transit advocates who know little about economics understand the fundamental concept of elasticity--the concepts of "choice riders" and "transit-dependent" refer to two different populations who express different elasticities with regard to their transit-using habits.  Choice riders express a high elasticity--meaning that their consumption (use) of transit is likely to change as the value proposition changes; if the fares go up or the frequency goes down, they stop riding, and if service improves, they may switch back to transit.  Transit-dependent riders express a low elasticity--they'll put up with a lot because they have no other choice, and conversely, improving service isn't likely to attract more transit-dependent riders, as those who need the service are already using it.  A third community to consider is the transit-averse:  those who won't use transit under any circumstances.  They also express a low elasticity, as improvements to the system are unlikely to entice them to increase their consumption (usage), which will remain at zero.

One interesting phenomenon concerning elasticity is that it goes up in a recession.  Even if the capacity remains adequate and the coverage remains the same, when a recession occurs, cuts to service are more likely to negatively affect ridership during hard times.  When a recession occurs and people lose their jobs, two things happen:  unemployed riders for whom transit demand was previously inelastic suddenly find it elastic, as they no longer need to be at work by a certain time.  And congestion on roadways decreases, increasing the relative value of driving for those who can drive (which is the majority of the population in most parts of the US)  .   This is why "death spirals" are a pressing problem for transit agencies during a recession--loss of revenue leads to service cuts which leads to loss of riders which leads to loss of revenue which leads to... you get the picture.  (When a transit agency finds itself in this situation, as TriMet appears to be, you had better hope that the pattern of panic/cut/cringe converges at a level well about zero).



Its all about the values

When publicly-operated rapid transit projects are proposed, there are often several reasons offered to justify the expenditure of public funds:

• Increasing coverage
• Increasing capacity
• Increasing service quality
• Decreasing operating costs
• Environmental outcomes
• Land-use outcomes
• Economic development

The first three are important to transit users (and potential users).  The others are important to other constituencies (the transit agency, the public at large, etc) and won't be considered further.  Whether any of these are important to a given rider or group depends on what the rider or group's goals are.  And if a person takes a more minimalist view of transit--s/he may not be interested in attracting riders to the system--and consider expenditures for that purpose a waste of money. While I can't point to research to back it up, it seems apparent that many of those who adapt the minimalist point of view are those for whom transit demand is most inelastic.  the transit dependent, who have every reason to be skeptical of proposed new projects--many of which will benefit some other community and adversely affect the particular service they depend on; and the transit-averse, who won't ride the system at all, and may view the entire enterprise as a big waste of money.

This dichotomy may affect one's answer to the question posed by Jarrett at the top of this article.   It's a common psychological phenomenon to project ones thoughts and beliefs onto others.  Thus, if an individual's personal demand for transit is inelastic (or one's own personal value system WRT transit focuses on tangible service parameters such as coverage, capacity, and performance, and disregards things like amenities or social acceptance), s/he may assume that this is true for others--and question the claim that improving transit quality may increase ridership.  Likewise, if a person's personal transit demand is highly elastic (or is motivated by factors specific to a particular mode choice), s/he may assume that increasing service levels (including by conversion to rail) will axiomatically drive up demand--and further assume that what is important to him/her, is important to everybody, thereby causing an overestimation of the induced demand.

The truth, of course, lies somewhere in between, and ought to be determined empirically rather than by ideological catfights between different communities and constituencies.