Intersection Timing

Another big issue brought up at the workshops is how the intersection timing across both 47 & 65 favors traffic going north and south. Residents that are actually trying to just get to the other side of town find themselves waiting endlessly.

So what’s up with split-phase intersections? Well, let’s define it first:

A split phase intersection is one where one side gets a green light and green left turn arrow, then the other side gets a green light and a green left turn arrow.

Here are the technical details behind split phase intersections: https://safety.fhwa.dot.gov/intersection/conventional/signalized/fhwasa13027/ch5.pdf#page=11

They aren’t known for their efficiency – they’re a band-aid for poor road design. But I think I’ve found one of the better ones which others should emulate.

Fridley’s Split Phase Intersections

There are several split-phase intersections in Fridley. MN-65 & Mississippi St. is the most notorious, however there are split-phase (or rough equivalents) at MN-47 & 57th and MN-47 & Mississippi.

Most of these are in place because of road geometry. The state highways (65 and 47) are so damn wide that there can’t be two left turn lanes running simultaneously without cars crashing head-on. 4-to-3 lane road diets could alleviate those problems, but until then let’s look at the signal timing – a software problem we could address today.

None of the split phase intersections work well for residents in Fridley, whether they’re driving, walking or biking. So let’s look a well-timed example to copy.

County Road 10 & Able Street

I used this intersection twice daily by car or by bicycle for 4 years. It is on the way to my kids’ day care provider. I didn’t like it at first… in my car when you leave Highway 65 and go on County Road 10 west, it’s the first signal you’ll encounter.

More often than not the signal would be green and then I’d see it change to red as I was approaching. I’d silently curse to myself (trying to watch my mouth as a new Dad). But after going this way about a dozen times, I realized something. I’m almost always going to see the light change from green to red because it’s constantly changing all the time. This is a good thing because it won’t be red for long for either the people on County 10 or Able St.

The first question traffic engineers will probably ask is “how much traffic goes through there?” It’s sees 20,000 vehicles per day on average. Keep in mind the times when I was using this intersection was always during rush hour, 7-8AM and right at 4PM.

So why not try it for a week or two? Signal timing is software, not hardware. Yes, 47 & 65 carry a bit more traffic (30,000/day), but if traffic backs up on 47 or 65 one of two things will happen:

1. MnDOT will change the timing back
2. People will find another way that is less congested

#2 is the option residents are shooting for. Remember when the 35W bridge collapsed? If I recall correctly, traffic was a little nutty for about a week, and then… Poof! Everyone found a different way about town and traffic wasn’t drastically worse than when 35W was wide open.

We should at least give this cheap-and-easy timing change a shot. Got any other ideas for these roads? Share them in the comments.