BRT on JBR, part one

BRT capacity to meet future demand.

I have expressed my concern that the efforts of the Town of Chevy Chase to promote Bus Rapid Transit on Jones Bridge Road (BRT on JBR) could have unintended consequences, in Will the BRT campaign backfire?. I closed that post with a promise to address the BRT vs. LRT issue in a future post.

Those of you who are interested in this BRT vs. LRT issue have had plenty of newspaper articles and blogs to follow. The discussion has been driven into hyperdrive by the Washington Post article Md Busway Promoted as Solution to Gridlock and by a Montgomery Gazette article Council member’s rapid bus system on transit table. If that is not enough, a guest blog by Delegate Al Carr in Just Up the Pike supporting BRT on JBR triggered a robust online discussion as other blogs quickly joined the discussion. A few of the most significant discussions are at Rebuilding Place in an Urban Space, Greater greater Washington, and Maryland Politics Watch.

I don’t want to rehash the whole BRT vs. LRT debate here. Nonetheless, there are some aspects of the BRT on JBR design option that are important to whether BRT on JBR is the best Purple Line option as the Town of Chevy Chase claims. I will describe discussions that occurred recently between M-NCPPC staff and MTA staff at the Dec. 8 Planning Board work session.

Demand vs. Capacity:

The issue of BRT capacity was discussed at the Dec. 8 Planning Board work session. The work session staff memorandum presented projected peak ridership estimates that showed the BRT will be at or near its full design operating capacity by 2030. In the most important Purple Line segment (i.e. the one nearest my home) at Silver Spring to 16th Street, the projected “Peak directional line load” is 1652 passengers/hour for the Medium Investment BRT, and 1858 passengers/hour for the High Investment BRT. MTA staff present at the meeting indicated peak load in east Silver Spring will be almost as high. MTA estimates the design BRT capacity to be 2100 passengers/hour. Since the capacity (2100) slightly exceeds the highest estimated demand (1858), it looks like we are “good to go”.

But the M-NCPPC staff has some reservations about the MTA capacity estimate that they describe in their staff memo. They have found what they consider to be more realistic studies on BRT capacity that indicate the Purple Line BRT design peak line load capacity would be 1800, not the 2100 MTA has assumed. The extended discussion between MTA staff and M-NCPPC staff at the meeting appeared to support the M-NCPPC staff concerns. MTA assumes 140 people per BRT vehicle with 15 vehicles in each direction per hour for the Purple Line estimate, but 120 people per BRT vehicle may be more realistic. MTA assumes it can inject extra “jumper” vehicles into to the Purple Line system at the peak hour to meet the demand. But there was agreement among the M-NCPPC and MTA staff during the discussion that the ability to introduce more vehicles is greatly compromised by the BRT Purple Line design that has the buses running on busy streets in traffic at the ends of this peak load section, in both downtown Bethesda and east Silver Spring. In short, you can’t just put a lot more buses out there if the buses do not have their own dedicated lane, because the street traffic will screw the bus intervals up and too many buses will screw up the street traffic if they have signal priority. The discussion can be seen on video, from the Planning Board agenda webpage. The discussion on Purple Line capacity was the first major issue taken up.

The give and take in the discussion about whether or not BRT will be over capacity in 2030 distracts us from the real capacity problem. During the Planning Board discussion Dr. Glen Orlin, Mont. Co. Council Staff Director, pointed out what I think is the elephant in the room when we talk about Purple Line capacity. The Purple Line AA/DEIS is required to measure ridership against year 2030 projections for consideration for funding by the federal government. But the Purple Line will only be 15 years old by 2030 under the most optimistic construction schedule. What will the demand be in 2050, at 35 years of age?? Does anyone doubt the demand will be much higher? What if the cost of gas goes up again soon, to even higher levels than seen recently, and transit demand grows faster than the models predict – in which case we will not even make it to 2030 before capacity is exceeded by demand?

It is nuts to consider building a legacy transit system with BRT if it is going to be at or near full capacity within 15 years of construction when it cannot be easily modified for higher capacity. In contrast the M-NCPPC staff memorandum shows the LRT Purple Line has the capacity to meet the 2030 demand. More important, both M-NCPPC staff and MTA staff appeared to agree during the discussion that LRT can be expanded much more easily than can BRT to carry the much higher demand likely to come beyond 2030.

I know this discussion doesn’t relate to the trail directly, but it does relate to whether the BRT part of BRT on JBR is a good idea. In the next post on this issue I will turn to another issue covered in the Dec. 8 Planning Board work session that is more closely related to the Trail, how the BRT on JBR alignment option measures up against BRT alignments on the Georgetown Branch Trail.

3 Responses to “BRT on JBR, part one”

  1. David Brook Salzman, Ph.D. says:

    Wayne writes, “It is nuts to consider building a legacy transit system with BRT if it is going to be at or near full capacity within 15 years of construction when it cannot be easily modified for higher capacity.”

    Certainly true. Which raises the question of what LRT supporters truly want, because the facts that rail objectively meets needs less well and obsolesces more rapidly have zero evident impact on their enthusiasm for it.

    If you work the numbers, you will find the BRT will not be anywhere near capacity in 2030. The MTA gave the Medium-Investment LRT $6.6 more operating funds than the Medium-Investment BRT in its projections, to preevnt an apples-to-apples comparison. If the BRT is funded at the same annual operating budget, it offers 50% more at-peak seats than the LRT and twice-as-frequent off-peak service, and this is after reducing the peak per-vehicle capacities used by the MTA to more industry standard numbers (10% lower for the LRT and 30% lower for the BRT).

    After adding in the capital upgrades to pay for overpasses (underpasses?) at Wisconsin, Connecticut, and Georgia, and tunneling under Woodmont and from 16th Street to East Silver Spring as needed, the BRT would offer (1) about $400 million lower capital cost; (2) faster incorporation of new engine technologies (since the rolling stock is replaced faster); (3) more frequent service at all hours, including twice as often off-peak; (4) more seats at-peak; (5) 3x less CO2 per passenger mile, and hundreds of times less mercury, sulfuric acid, and particulates; (6) more riders; (7) identical service speed; (8) absolute savings in pollution (with just 8 new riders on average) compared to cars left behind, versus no savings ever in pollution for the LRT compared to cars left behind.

    None of this is complicated. The question is what LRT supporters truly want, because when the “facts” they cite as premises turn out, on close inspection, to be bogus, their argument continues to barrel along shamelessly. I find that odd.

  2. silverspringtrails says:


    Increasing BRT capacity may be possible to the extent that BRT can be isolated from traffic by getting more bridges and tunnels and getting dedicated lanes. As the staff discussion at the Planning Board work session indicated, the ability to put more BRT vehicles out there with shorter headways is limited by interference with traffic, and as you go more toward dedicated lanes and grade separation the more that limitation eases.

    I would point out the neighborhoods along Jones Bridge Road are already upset at the impact of BRT when there are no bridges or tunnels, and the east part of the JBR is shared, not dedicated, BRT lanes. Wait till they hear you want bridges and/or tunnels with ramps, and taking r.o.w. at the east JBR section to carve out dedicated BRT lanes.

    But you can’t just stop with bridges or tunnels at Connecticut Ave. and Georgia Ave. You will need to get the BRT onto dedicated lanes and crossings east from Silver Spring too, so the BRT vehicles can maintain their headway and separation on the whole corridor. That means the capital costs will rise much more than you suggest because there are many areas east of Silver Spring where the Purple Line is on shared lanes or crossing busy roadways at grade.

    The staff discussion indicates LRT is not as sensitive to this issue. Several LRT vehicles can be joined to carry the same number of riders on one train as on 4 or 5 BRT vehicles. The LRT conflict with traffic only increases marginally was the train gets longer. But each additional BRT vehicle creates its own complete new interference, so that 5 BRT vehicles have a much heavier traffic interference than one train. I’d much rather deal with one three car LRT coming through every five minutes than have a BRT vehicle coming through every minute, if I’m a driver trying to share a traffic lane or intersection.

    I don’t think increasing BRT capacity in this corridor will be as easy as you suggest.

    Wayne Phyillaier

  3. David Brook Salzman, Ph.D. says:


    The problem with your argument is that it doesn’t hold up when one uses real numbers instead of hand-waving. Your bio says you’re an engineer, but a quantitative analysis reaches different conclusions from yours.

    LRT trains are limited on the Purple Line to two rail cars by the size of the stations. Try to use 3 cars and much of the line’s civil engineering (and traffic interference expectations) change for the worse. The alleged “4 or 5″ ratio of vehicles has no foundation.

    An LRT train would run every 180 seconds on average at peak, not the 300 you cite. The BRT would run every 75 seconds on average to carry the same number of seats/hour, or every 60 seconds at-peak (and twice as often off-peak) for the same operating cost.

    Key point: The MTA now admits that outright preemption of traffic signals is unacceptable because it causes more traffic disruption than it cures, so the LRT running at-grade will include traffic signal delays as well as built-in delays for waiting half a signal cycle. BRT buses on the same route experience exactly the same average delay stuck waiting for signal cycles. The apparent bunching of buses (“Why do buses come in threes?”) is just an artifact of sampling more often, not a delay any less harmful to trains. You appear to be over-perceiving the interference by the BRT of an at-grade intersection, whose comparative effect is the traffic displaced by a vehicles themselves (merely a 2nd or 3rd order effect at these traffic densities and flows).

    BRT and LRT are equally penalized by at-grade intersections; and they benefit equally from avoiding at-grade intersections.

    The BRT is so much less expensive than the LRT that the proper apples-to-apples comparison would give it comparable capital costs as well as operating costs, hence dedicated lanes and tunnels in a number of hotspots where the LRT lacks them. Even with lower capital cost, this translates to faster average speed, more seats per hour, less inter-vehicle waiting time, and by any measure except so-called “snazziness,” better service. Add to this the lower pollution, lower operating costs, and ability to serve more customers, and one has to wonder why anyone who actually understands the physics and engineering would prefer an LRT. But, the public has spoken, and snazziness won out.