What is the impact of the proposed Honolulu rail project on future traffic?

It’s a pretty straightforward question, and an important one for the project. Opponents have repeatedly pointed out that traffic will be worse with rail than it is today. Planners have said it’s more appropriate to compare future traffic levels with rail against future traffic levels without rail.

Speaking Oct. 18 to the Rotary Club of Honolulu, Mayor Peter Carlisle said rail “will take an estimated 40,000 vehicles off our roads each weekday in 2030.” (He made a similar remark after his Jan. 24 press conference upon his return from Washington D.C., but we don’t have the audio.)

Watch the video here, courtesy of Robyn C. Ocepek on Vimeo:

Skip to the 9:15 point to listen to Carlisle make the following statement:

“We want to talk a little bit about some actual facts. Rail will ease future congestion — without rail, the congestion will be far worse. It will take an estimated 40,000 vehicles off our roads each weekday in 2030; especially during rush hour traffic. There will be zero traffic congestion in the future for those who ride grade-separated transit.”

Here’s a screen capture of the slide he’s reading:

His language — touting his talking points as “actual fact” — begged for a Civil Beat Fact Check.

We came up with three important questions we hoped to address with our work:

  • How did Carlisle come up with that estimate?
  • How does it fit in with both ridership projections and industry standards for measuring traffic impact?
  • Is it backed up in the Environmental Impact Statement or any other documents?


The answers to the first and third questions were pretty much the same. (We didn’t dig into the second question. It turned out that it wasn’t essential to getting to the main focus of this Fact Check.)

The mayor asked the Honolulu Authority for Rapid Transportation to respond. It provided the following statement:

The info can be found in Table 3-12 of the FEIS. It shows 3,003,400 daily person trips by private auto in 2030 for a “no-build” option; and  2,952,200 daily person trips by private auto in 2030 with the rail system. The difference is 51,200 daily person trips by private auto.

To obtain the number of vehicles, an occupancy factor was applied to the 51,200. So essentially, 51,200 was divided by 1.25, which is the average number of occupants per vehicle. That figures comes to 40,960 (hence the 40,000 cars off the road daily).

It is also important to note that the EIS, including its tables and projections were approved by the FTA. The FTA has been doing this for decades and would not have approved this if they had accuracy concerns.

The FEIS is the primary planning document for the rail project and it’s vetted by the federal government and independent transit experts. That’s not to say that it’s going to be 100 percent accurate, but it is the most comprehensive and rigorous analysis of the project available.

It’s true that the FEIS has those numbers (or similar ones) in it. Chapter 3 of the document does have the 3,003,400 (no-build alternative total person trips) and 2,952,200 (total person trips with rail in 2030) numbers.

Under the heading “Vehicle Occupancy,” the FEIS states:

Average vehicle occupancy (AVO) data were last collected by the Hawaii Department of Transportation (HDOT) in 1998. The four monitoring stations in the study corridor are Moanalua Freeway at Moanalua Stream Bridge, Kalanianaole Highway, Pali Highway at Tunnel No. 1, and Likelike Highway. During the a.m. commute period (5:30 to 9:00 a.m.), traffic using Moanalua Freeway at Moanalua Stream Bridge had the highest commute period AVO in the study corridor (1.28 persons per vehicle). Traffic on Pali Highway at Tunnel No. 1 experienced the highest peak-hour AVO in the study corridor at 1.31 persons per vehicle.

If you divide the 51,200 passenger trips by the highest average vehicle occupancy of 1.28, that yields the mayor’s number of 40,000 exactly. (The Hawaii Department of Transportation (HDOT) told Civil Beat Monday it has no new data for average vehicle occupancy.)

But that’s where things get confusing, and where HART’s, and the mayor’s, interpretation of the numbers may be misleading.

Dividing the number of person trips by the average number of people per vehicle would yield the number of vehicle trips, not the number of vehicles. For the two to be the same, each vehicle would have to make one, and only one, trip per day. That’s just not how things work.

The mayor didn’t say “trips.” He said “vehicles.”

“A vehicle trip would be from Point A to Point B,” HDOT communications chief Dan Meisenzahl told Civil Beat. “So if you go from home to work and back, that would be two trips.”

A look at some historical data is instructive. The same table in the FEIS that has the no-build alternative and with-rail trip figures also has a number for the total daily private automobile trips in 2007: 2,424,500. That’s about four “trips” for each of Oahu’s 599,309 registered passenger vehicles that same year, according to the 2007 State of Hawaii Data Book chapter on transportation.

So if you looked at his statement as about actual vehicles as opposed to vehicle trips, the numbers would be much lower. Even if every driver were to go straight from home to work and back each day, that would drop the number of vehicles removed from the island’s roads each weekday in 2030 from 40,000 to 20,000. If the average of four trips per vehicle per day from 2007 holds, the number of vehicles removed from roads by rail would drop to 10,000.

That’s a small number compared to the total number of vehicles that will be on the island in 2030, just as the estimate of 40,000 vehicle trips per day is small compared to the 3 million total daily vehicle trips.

But the interim executive director/CEO of HART defended the mayor’s statement, pointing out that Carlisle was talking about “taking vehicles off our roads.”

“The way we use it in context, ‘cars off the road’ is the same as ‘number of trips,'” Toru Hamayasu told Civil Beat.

“It may not even be 20,000 cars,” he said of the reduction in the number of cars. “It could be one car making 40,000 trips. We don’t care how many cars are making trips. What’s important is how many trips are being made.”

Bottom line: *This is a case where what’s being said and what’s being heard may be two different things. The mayor clearly has a basis in fact for what he’s saying. But the public should understand that there will not be 40,000 fewer vehicles on Oahu as a result of rail, which is the way the mayor’s words could sound to some. The mayor would have been clearer if he had used the word “trips” somewhere in his statement. That’s why the grade is “Mostly True” and not “True.”

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