Widening of I-75 to begin this summer in Oakland county

[impala096]

MDOT is planning on building a Diverging Diamond interchange at Big Beaver Road as part of the project...


Instead of a DDI, a Parclo interchange with contraflow left turns seems like it would have been a good alternative. Below are models of each interchange design:

[DTWflyer]

Oh boy, that is going to confuse the heck out of people.

[mjlo]

Originally Posted by DTWflyer

Oh boy, that is going to confuse the heck out of people.

It's really not that bad, they did the same style interchange at a busy interchange near Grand Rapids and its pretty easy to navigate.

[Geo-Aggie]

I've used the Diverging Diamond before. In fact there are quite a few where I lived most of my life. They're really good and not at all confusing. People may be cautious on their first use but they'll have the hang of it immediately and it will absolutely decrease both congestion and traffic incidents.

[MS313]

Originally Posted by Geo-Aggie

I've used the Diverging Diamond before. In fact there are quite a few where I lived most of my life. They're really good and not at all confusing. People may be cautious on their first use but they'll have the hang of it immediately and it will absolutely decrease both congestion and traffic incidents.

I hope your right. Because right now it looks worse then the mixing bowl, and it looks like they have people driving on the opposite sides of the road too.

[impala096]

Originally Posted by Geo-Aggie

I've used the Diverging Diamond before. In fact there are quite a few where I lived most of my life. They're really good and not at all confusing. People may be cautious on their first use but they'll have the hang of it immediately and it will absolutely decrease both congestion and traffic incidents.

By adding traffic signals that stop both directions of travel between the major mile roads (which is what the Diverging Diamond does), you essentially kill signal progression along Big Beaver. This is what the signal progression looks like currently and how it would look when the Diverging Diamond is constructed. With the DDI, you can only maintain good signal progression in one direction of travel along Big Beaver.






Not only would the Diverging Diamond mess up signal progression, but many Diverging Diamonds have a regulatory speed limit of just 25 mph. There is an example of a DDI along a 6-lane boulevard outside Nashville that has a regulatory speed limit of 25 mph that lasts for 2610 feet. It takes 71 seconds to travel 2610 feet at 25 mph versus 39 seconds when traveling at 45 mph. I believe MDOT is planning on signing the Big Beaver DDI for 25 mph and that alone will add ~30 seconds of delay assuming drivers are traveling the speed limit (and if they aren't traveling the posted speed limit, maybe it will become a popular speed trap for Troy PD). Here’s that Nashville DDI I mentioned above:

https://www.google.com/maps/@35.9833.../data=!3m1!1e3

Drivers along Big Beaver getting stopped at more red lights… subdivision speed limits along a major 6-lane suburban boulevard (so drivers can apparently admire MDOT’s new interchange)…. I don’t necessarily see how the diverging diamond will be an improvement.

[impala096]

^My proposed interchange fits in the same footprint as the current configuration. Instead of diverging all traffic, you only diverge traffic that is actually entering onto the freeway. Good signal progression is maintained because the traffic signals only stop one direction of travel and you would be able to keep the 45 mph speed limit along Big Beaver. That to me sounds like less delay/congestion than the DDI design MDOT selected...