Improving LRT Signal Timing in Downtown Minneapolis

Although St. Paul’s traffic signals deserve most of the blame for slowing the Green Line, there’s room for improvement in Minneapolis as well. To be fair, Minneapolis deserves praise for its signal timing through the University of Minnesota campus, where trains are seldom delayed. They’ve also established a very good progression for westbound trains from the city limits to the Prospect Park Station, including the right turn from University Avenue onto 29^th Avenue SE.

In downtown Minneapolis the results are mixed. As in downtown St. Paul, part of the problem is that intersections that previously split green time between two streets now have that time split three ways—the LRT, the cross street and auto turn movements across the LRT with the LRT stopped. With one-third less green time available, keeping the LRT moving is a greater challenge. This is the situation at 3^rd Avenue N., 2^nd Avenue N., Nicollet Mall, Marquette Avenue, Park Avenue and 4^th Street-Chicago Avenue.

After examining the city’s own reports on traffic volumes (including intersection turn movements by hour of the day), I’ve concluded that there are opportunities to give more time to LRT in downtown without unreasonably disrupting auto traffic. The basic premise is: if auto movements don’t need all the green time allocated to them, that time should be reassigned to LRT. In some cases, the auto movements are small enough that their signal phases can even be preempted without causing undue delays.

The Green Line opening is the catalyst for making this proposal, because it has doubled the number of people traveling on 5^th Street. LRT now carries many more people than the autos on most of the streets that cross the tracks. LRT also has to compete for green time with the small number of autos that share 5^th Street. They currently get a third of the green time at several intersections, despite carrying a tenth of the LRT’s volume. For those reasons it’s time to take a fresh look at 5^th Street signal timing.

Starting at Target Field Station, let’s take the intersections one at a time. To get an apples-to-apples comparison, each LRT passenger is given the same weight as an automobile.

3^rd Avenue N.

3^rd Avenue N. frequently stops the trains. The signal cycle is divided into three phases, for 5^th Street and LRT, for 5^th Street left turns across the tracks onto I-394 and for 3^rd Avenue N. The left turn and 3^rd Avenue N. movements are tiny compared to the LRT, or to any other intersection in downtown. Left turns across the tracks amount to only 5 per hour in the midday and 22 per hour in the PM peak. Traffic on 3^rd Avenue N. is only 8 cars/hour in the AM peak, 31 in the midday and 69 in the PM peak. That may seem like a lot, but it’s only one car per minute. They’re holding up trains for one car per minute?

2^nd Avenue N.

2^nd Avenue N. is a three-way intersection. It’s busier than 3^rd Avenue N. Auto and LRT volumes are about the same, but that’s only about 5400 cars and buses on 2^nd Avenue compared to 3900 LRT passengers. Although the counts are about even, a review of the auto counts by time of days show only 3 cars per minute on 2^nd Avenue in the AM peak, 2 per minute in the midday and 7 per minute in the PM peak. Those are spread over two traffic lanes, so it’s really 3.5 cars per lane per minute.

The other source of delay at this intersection is the 5^th Street auto traffic, which crosses the tracks here. It amounts to only 2 cars per minute, except in the PM rush hour, when Garage B empties into a single lane on 5^th Street. Then volumes reach 5 cars per minute.

1^st Avenue N.

1^st Avenue N. green time is only split two ways. 1^st Avenue carries twice the traffic as 5^th Street in a single lane, so there’s really no room for improvement.

Hennepin Avenue

The same goes for Hennepin, which is the busiest street the LRT crosses. Including 5200 daily bus passengers, Hennepin carries twice the volume of 5^th Street. No change possible here. Thankfully, Hennepin has only two signal phases, so delays aren’t bad.

Nicollet Mall

Nicollet Mall is a 3-way signal. The Mall is bus-only and 9000 bus passengers cross 5^th Street compared to about 10,700 LRT passengers. We don’t want to slow down the buses. However, there are only 2500 daily autos on 5^th Street, 2-3 per minute, so that phase can definitely be squeezed.

Marquette Avenue

Marquette Avenue and 2^nd Avenue S. are the paired contraflow bus lanes that carry an enormous volume of passengers on the rush hours, so they’re off limits for peak period cuts to the cross street. However, in the midday there are few buses and Marquette averages only 5 cars per minute divided between two lanes (2.5 cars/minutes/lane), so there’s room for more LRT green time. Marquette is a 3-way light, and the 1600 daily cars on 5^th Street get more green time than they deserve (only 3-7 cars per minute), so there’s an opportunity.

2^nd Avenue S

2^nd Avenue S. is a 2-way light that seldom stops the trains. As with Marquette, rush hour buses need all the green time they currently receive, but off-peak hours offer an opportunity to help the LRT. Like Marquette, In the midday, 2^nd Avenue S. sees only 5 cars per minute divided between two lanes.

3^rd Avenue S.

3^rd Avenue S. has 11,100 cars and no buses. That’s fairly busy (5-7 cars per minute per lane) and more LRT green time may be difficult to justify, even though 5^th Street crossing 3^rd Avenue S. is now up to 22,500 LRT passengers.

4^th Avenue S.

The numbers for LRT versus autos improve greatly at 4^th Avenue S. because the Government Center Station passengers have boarded. Now it’s 28,200 LRT passengers plus 2239 cars on 5^th Street (total 30,400), against 8500 cars and 638 bus passengers on 4^th Avenue for a total of 9138. These lopsided volumes argue for signal preemption.

5^th Avenue S.

5^th Avenue S. is somewhat busier, 9800 cars and 1455 bus passengers (total 11,255). Auto volumes vary from 7 cars/minute in the midday to 17/minute in the PM peak. Although that may seem high, there are three through traffic lanes on 5^th Avenue, so each lane is handling about 6 cars/minute. It would not delay autos to reassign more green time to 5^th Street, which has 28,200 LRT passengers and 2239 cars total 30,400. 5^th Avenue is another 2-way signal, so there’s more green time to reallocate.

Portland Avenue

It’s even better at Portland Avenue, a 2-way signal that has only 5246 cars and no buses. That makes it almost as low as Victoria Street in St. Paul, where the city is reluctantly experimenting with full preemption (which is working well for LRT, it turns out). LRT combined with autos has almost 6 times the traffic volume.

Park Avenue

Park Avenue is a 3-way signal with 6700 cars and no buses, now that the 94 express has been rerouted. The Park Avenue phase has only 5-11 cars per minute, spread over three lanes, therefore lowering the per lane count to no more than 4 cars/minute, even in the PM rush hour. There are 4 LRT passengers for every car on Park. The right turns from 5^th Street onto Park, which get their own phase, amount to only .5-1.5 cars per minute, a tiny volume that could certainly be preempted.

4^th Street and Chicago Avenue

The situation at 4^th Street and Chicago Avenue, where trains cross diagonally through the intersection, is somewhat more complicated. This has proven to be a real bottleneck for trains. When Blue and Green Line trains to Minneapolis converge at the junction at the same time, one has to wait for the other to clear. The first train then hits a red light at 4^th/Chicago that can last two minutes. Once clear of the intersection, there’s the Downtown East Station stop, followed by the light at 5^th and Park. This has turned into a cascade of delays for both lines.

Chicago has only 3300 cars (3-5 cars/minute) and will never be a busy street. Reducing Chicago’s green time, even preempting it, is probably the best way to reduce LRT waits.

4^th Street has 6800 cars, along with 2083 bus passengers. 4^th Street car volumes decreased dramatically when Washington Avenue was closed through the U of M campus. Bus volumes are also down sharply, because Routes 16 and 50 were replaced by the Green Line. Bus passengers on 4^th Street declined from 5210 before the Green Line to 2083 now.

However, more express buses and car traffic may soon be shifted to 4^th Street to access the new on-ramp to northbound I-35W under construction near Seven Corners. If so, bus passengers will rise by 1500 per day, all in the PM rush hour. If half of the car traffic to northbound I-35W is diverted from Washington Avenue, 4^th Street’s car volume will increase by 5000 to 11,500 plus 3600 bus passengers, totalling 15,100. That is divided between two lanes. If my projection is correct, 4^th Street will see 4 cars per lane per minute. That rate would permit more green time for LRT.

To summarize 4^th & Chicago, I project that their combined auto and bus total will be 18,400 per day, assuming all possible buses are rerouted to the new on-ramp. However, LRT volume is 36,300, thanks to boardings at the Downtown East Station. That 2 to 1 ratio, plus the potential to reduce train delays, argues for more LRT green time.

Time of day variations

Most of the streets that cross the LRT are only busy in the rush hours, with the PM rush hour being noticeably heavier than the AM. Even where preemption cannot be justified in the rush hours, it should be coinsidered during the off-peak. I was recently at 5^th and Marquette at 9 PM on a Saturday and watched a train wait at both 2^nd Avenue S. and Marquette, even though there was no cross traffic at all. That’s unnecessary. The result will be much faster LRT travel times during the large majority of service hours, hopefully permitting a train to be removed from the schedule, a major savings.

Is priority counterproductive?

Priority can only shorten a red light or lengthen a green by a modest amount. I’m starting to suspect that priority can’t effectively move the LRT through downtown when the LRT green phases are too short. This is particularly true since the added Green Line trains are producing calls for priority every couple of minutes.

I watched the signals on 5^th Street to get a better idea of how the LRT signal phases compared with those for autos at each intersection. Disclaimer–Not having access to the city’s actual timing programs, my conclusions are empirical and certainly not precise. Even so, I don’t think my conclusions are too far off.

At the 2-phase intersections (1^st Avenue N., Hennepin, 2^nd Avenue S., 3^rd Avenue S., 4^th Avenue S., 5^th Avenue S. and Portland) the LRT “Go” signal was on whenever the light was green for 5^th Street. That’s good as far as it goes, but out of a 110-second signal cycle, the LRT seemed to get about 30 seconds, or less than 30 percent of the green time. Giving the LRT half the 110-second cycle would double what they presently receive.

30 seconds was generous compared to the 3-phase intersections. The LRT would sit through the other two phases meant for autos, then have maybe 15 seconds of green time, less than 14 percent of the cycle. It appeared that the LRT phases were intentionally only long enough for the train to clear the intersection. If LRT simply received 1/3 of the time, it would more than double to 36 seconds.

It occurred to me that active priority with small LRT windows may be self-defeating. With so many trains moving in both directions, it’s not possible to thread that particular needle, unless the hole is made much larger. Longer fixed LRT green phases with no priority might produce fewer delays than at present.

Conclusions

LRT in downtown Minneapolis was never given green time proportional to the number of people it moves through an intersection.

The opening of the Green Line has greatly increased LRT’s share of the people passing through downtown intersections. At most intersections, LRT transports many more than do automobiles, yet it still receives a small minority of the green time.

At many intersections, green time is wasted on low volume auto phases that could be shortened or preempted with little or no harm to auto flow.

Signal priority with extremely short LRT green time (the current practice at 3-way intersections) is less effective at moving LRT’s than longer LRT green time without priority. Of course, both would be even better.