If PennDOT rocked the boat when it began building roundabouts, expect things to get even stranger when diverging diamond interchanges start appearing in the midstate over the next few years.

Two such interchanges -- one at the Shrewsbury exit of I-83 in York County and a second one near Ephrata in Lancaster County -- are slated to begin construction in 2019. The first diverging diamond interchange in Pennsylvania, on I-70 in Washington County, was completed earlier this year.

Diverging diamonds are a departure from standard diamond or clover leaf designs -- instead of making left turns across oncoming traffic to enter highway on-ramps, they are designed to weave traffic through the interchanges, eliminating cross-traffic left-hand turns, as the following image illustrates:

This diagram shows how traffic flows through the diverging diamond interchange in Washington County. The design 'weaves' traffic, eliminating left-hand turns across oncoming traffic.

Diverging diamond Interchanges have become somewhat popular in the Midwest. Missouri, which constructed the first diverging diamond interchange in 2009 near Springfield, has built 19 over the last eight years.

"They really do work," said Bob Brendel, with the Missouri Department of Transportation.

Brendel said that while a diverging diamond interchange isn't the best option for every situation, "if it's an intersection without a heavy number of turning events, then they work really well," he said.

"They have a lot of advantages and are very adaptable . . . and they are a lot cheaper than a normal interchange," he concluded.

In York County, rapid growth in the Shrewbury area has caused congestion at the I-83 interchange to become a fact of life. A few years ago PennDOT began examining possible changes and upgrades to the intersection designed to eliminate the backups.

Compared to a traditional interchange, PennDOT's analysis showed that using a diverging diamond at that location would significantly reduce the number of potential crash points as well as result in a more continuous flow for traffic.

In Lancaster County, PennDOT is holding a public meeting this evening from 6 to 8 p.m. at the Ephrata Pioneer Fire Company to show the design to the public.

That interchange would link routes 322 and 222 and could begin as early as fall of 2019, depending on funding availability.

The following video, created for PennDOT, shows how a diverging diamond interchange works:

Admittedly, diverging diamond Interchanges can be a bit of a tough sell at first to the public.

"Peoples first reaction is: 'What are you smoking?,' " Brendel laughed. "But once they see it in operation people change their minds very quickly."