Thursday, June 29, 2017

BRT vs. Traffic Lane, Part 3

Continuing our series on BRT vs. Traffic Lane (Part 1, Part 2), another exploration how how the two compare. Mike Brown observed that:

  1. A 5-minute, fully loaded BRT would carry about as many people as a standard Arterial lane
  2. Unless you can trust that you can fully load each bus for an hour, then a 5-minute BRT will not move as many people as standard cars would.
  3. That's not necessarily a reason to go with cars.  Cars create car dependency, and they max out in what they can carry, but BRT can be increased to more than 5-minutes.
  4. "BRT" need not be a single route. In many downtowns, some block segments have a bus each minute, and sometimes more often.  
  5. Dedicating a lane exclusively to buses in these cases will result in more people per lane, assuming most buses are quite full.
  6. If automated vehicles and vehicle sharing begin to overtake private ownership, it is possible to imagine lanes where auto occupancy might reach 4 or more passengers carried in "minivan"-type vehicles.  In this "jitney-like" transit scenario, lanes even outside downtowns can start to carry far higher numbers than 5-minute suburban BRT," which is very aggressive service for suburbs.

Mike came up with the following numbers:


I'll add a few comments to what Mike has said.

1) I don't think it's physically possible to run 60 buses an hour, even dedicated bus pullouts. That would require a bus to decelerate, board, rejoin traffic, and accelerate. Even with elevated platforms, off-board fare collection and multi-door boarding, I think that would be a hard standard to achieve. And even one late bus would make all the buses in the queue later, and congestion would ripple down the line.

 The really serious BRT routes (Gold Standard) have four lanes: A curbside lane (to reduce time spent re-entering the travel lane) used for boarding, and a bypass lane. This seems to permit operations at headways as low as a minute and a half. But that would be four lanes, and outside our scope of analysis. Hit with capacity constraints, the current solution is to make a bus more train-like, but adding another unit, using double-articulated buses rather than just articulated buses. Double-articulated buses with capacities up to 180 are currently in use in Utrecht. Volvo has a 300 person capacity bus that is being tested on the TransMilenio.

2) Rare is a system that could load such a bus so heavily. But it might be possible. Daily ridership on route 830 (the route that the Provo-Orem BRT is to replace) reached 3,000 per day. The BRT was projected (in 2011) to have 12,900 daily riders. Assuming 10% of ridership takes place in the hour of the morning peak., that's 1,290 riders. Assuming the planned five minute headway is used, that's about 107 riders per bus. Or course, they won't all be on the bus at the same time. But it does suggest that the Provo-Orem BRT will be pretty heavily used. In 2030, the BRT is projected to have 16,100 daily riders, or about 137 riders per bus. Again, they won't all be on the bus at the same time.

3) BRT does scale better. Moving to a double-articulated bus would boost capacity to 120. At five minute headway, such a bus could carry 1400 persons per direction per hour , greater than a major arterial at 5pm. Alternately, just adding 3 more buses (to boost headway to once every 4 minutes an hour) increases it to 1400 persons per direction per hour. A bus every four minutes seems like something a single lane could manage. TRAX puts a train through an intersection every 5 minutes regularly (400 S. and Main). On 'crush load' (game) days, it might be as high as double that.

4) Branded Bus Corridors are a great idea. But they are only as long as the 'rainbow' portion of the corridor, where multiple lines overlap. Beyond that, you have to transfer. TRAX is a 'rainbow' corridor from 2100 South to Courthouse station. For trains with limited amounts of guideway, service laps are almost inevitable. But for buses, I'm not sure about inter-lining services: Does it just add more confusion? I think it only really works when buses are converging on a termini. I don't see it on the Salt Lake County or Utah County map, but you can see where one should be branded on the downtown Salt Lake Map: State Street from 5th South to North Temple, and thence west along North Temple to 300 West. All of North Temple could be branded, and both 200 South and 400 South might also be candidates.

5) The key question is not "Will the buses be full?" but "When will the pavement carry more people as a bus lane than as an automobile lane, during the peak hour." Not at five minute headway and 90 person loads, but at 100 persons/bus (at 5 minute headway) or 80 persons per bus (4 minute headway), a bus edges ahead. Based on the 2030 numbers, it seems likely that a BRT is a better long-term investment than a traffic lane.

6) A full discussion on automated vehicles is going to require a full blog post.

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