My Twitter feed has been abuzz again this weekend. This time with news of a study that shows a reduction in auto traffic (and emissions) following startup of a light rail line (in Salt Lake City).

This is apparently a first. Not having a demonstrated result like this has always been an arrow in the quiver of rail skeptics. I’m sure they’ll find ways to dispute this study… or just call it an outlier.

While I’m happy to see this, I’ve always thought this was an elusive thing to show, primarily because any passengers diverted from their cars were likely to be replaced from a pool of latent demand (I strongly suspect that Highway 26 in the Portland region works this way). So High Capacity Transit’s big benefit was in absorbing new demand in a corridor, not in diverting existing demand.

But maybe, and I’m just guessing here, in the light of declines in driving nationally, the pool of latent demand is diminished and we can actually show HCT taking demand away from SOVs. Wouldn’t that be nice!


4 responses to “Validation?”

  1. Is it possible that theres two types of demand for roads- elastic and inelastic? Im thinking of the difference between going to work, vs random side trips.

    If you commute to work, then you probably dont have a choice about how much you travel- you have to make that trip every week day, twice a day. On the other hand, a weekend jaunt to the coast can easily be avoided or expanded depending on how bad the traffic is. So a light rail line that follows commuting routes could reduce traffic by switching commuters from road to rail, but if it doesnt, the drivers it gets off the road will quickly be replaced by induced demand.

    • Charlie,

      The “random side trips” that LRT captures — mostly because folks live right alongside it and only have to transfer at most once — are often in the middle of the day or during the evening. Such trips made in the morning peak are almost non-existent. As such, their diversion to LRT really contributes nothing to any reduction in congestion that the trains may provide except perhaps a bit in the PM peak.

      High capacity transit is good for two things: in almost any city with significant peak hour corridor congestion it can “chop the top off the peak”. In that it basically competes with reserved lane express buses and can’t be justified unless there is right of way available to the trains that doesn’t work for buses or volumes which would make bus operation unreliable and expensive.

      An example here is Portland is the Robertson Tunnel. Such a facility would never have been built for buses, so they’d still be caught in the epochal congestion on the Sunset; there’s no room for a busway along it.

      In any case, LRT diverts only a relatively small extra proportion of auto trips than does high quality express buses.

      However, the second affect of HCT is to produce a “string of pearls” along its route IF GOVERNMENT WILL ALLOW IT. Where it does so it genuinely reduces automobile trips by eliminating the need for them. Over time both residences and work locations cluster around the train line, making it a “one-seat” ride for an ever greater number of people.

      That is the best way for commutation congestion to be reduced. As long as an urban region is smear sprawl without dense nodes transit will always suffer in comparison to driving.

  2. That study was for a specific destination (a university) where that university handed out hundreds of free passes for its employees to use it.

    Salt Lake city has nothing in common with any large city on the west coast.

    It’s nothing but light rail fanatics grasping at straws.

    Furthermore the only reason driving is declining is the price of gas, it has nothing to do with public transit

    • The only reason? That’s a pretty bold statement, considering you gave nothing to back it up.

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