1/20/2015 D6 Traffic Office Ashley Roup

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I-90 and 4th NW Interchange Austin, MN

Background

The I-90 and 4th NW Interchange is located in Austin, MN. Figure 1 shows the location of the interchange.

Figure 1: I-90 and 4th St NW Interchange

The interchange consists of one intersection with a traffic signal, for westbound off-ramp traffic to 4th St NW and through traffic on 4th St NW, on the North side of 4th St NW. Just north of the intersection with the traffic signal are vehicles turning left onto I-90 westbound on-ramp. On the south side of 4th St NW are vehicles turning left onto I-90 eastbound on-ramp and vehicles turning left and right onto 4th street coming from I-90 eastbound off-ramp.

Field Observation

4th St NW

I-90

1/20/2015 D6 Traffic Office Ashley Roup

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A field observation was conducted between the times of 3:30pm and 4:30pm on January 14th. The main movements of concern that were observed in the field at this interchange were 4th St NW southbound left turn to I-90 eastbound on-ramp (1), I-90 eastbound off-ramp left turn onto northbound 4th St NW(2), and northbound 4th St NW left turn to I-90 westbound on-ramp (3). The main movements are shown below in Figure 2.

Figure 2: Main Movements Observed

4th St NW southbound left turn to I-90 Eastbound on-ramp (1)

The furthest the queue developed for left turn movement was seven vehicles. For that seventh vehicle to turn it took 43 seconds to turn. Typically, the queue was approximately three vehicles. The left turn never queued backed into the lighted intersection to the north. Most vehicles had reasonable gaps in traffic to make the left turn. Some vehicles had to quickly turn left to make the gap, which could be more dangerous in unfavorable road conditions. The through traffic going north on 4th St NW never queued back from the lighted intersection far enough to block the left turn movement. Figure 3 shows the queuing of vehicles that are making the left turn to go onto the I-90 eastbound on ramp.

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Figure 3: 4th St NW southbound left turn to I-90 Eastbound on-ramp

I-90 Eastbound off ramp left turn onto northbound 4th St NW (2)

This movement is perhaps the most dangerous movement observed. Vehicles turning left to go on 4th St NW had a hard time turning because the vehicles coming from south bound 4th St NW to turn onto eastbound I-90 (1) were blocking them from turning if there were more than 2 vehicles in the turn lane. Also, when the vehicles would turn left to go northbound 4th St NW they would have to go behind the vehicles turning left to go to I-90 eastbound (1), which made it hard for vehicles going northbound on 4th St NW to see the vehicle turning. While observing only 5 vehicles made this movement, but all five had difficulty making the turn and three of the five almost hit vehicles that were going through onto 4th St NW. This movement never queued more than two vehicles. Figure 4 shows a SUV turning left onto 4th St NW behind vehicles turning left onto I-90 eastbound on-ramp.

1/20/2015 D6 Traffic Office Ashley Roup

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Figure 4: I-90 Eastbound off-ramp left turn onto northbound 4th St NW

Northbound 4th St NW left turn to I-90 Westbound On-ramp (3)

For vehicles turning left onto I-90 westbound on-ramp (3) there is no turn lane, so traffic continuing on 4th St NW north in the left lane had to wait for that vehicle to turn left before they could proceed. This would cause vehicles to queue back into the lighted intersection. When vehicles that were continuing straight on 4th St NW north saw a vehicle ahead of them turning left onto the on-ramp the vehicles would try to quickly move to the right lane last second. During the observation there were one near miss when a vehicle tried to get in the right lane last second and there was a vehicle behind them in the right lane. Figure 5 shows vehicles queuing behind a vehicle turning left onto I-90 west on-ramp.

1/20/2015 D6 Traffic Office Ashley Roup

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Figure 5: Northbound 4th St NW left turn to I-90 Westbound On-ramp

Other Observations

On the southwest corner of the interchange is a Burger King. Vehicles turning left onto 4th St NW from Burger King had a hard time finding a safe gap to turn. The longest observed time it took to turn left out of Burger King was 53 seconds. Figure 6 shows the location of the Burger King.

1/20/2015 D6 Traffic Office Ashley Roup

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Figure 6: Burger King Location

A lot of Pedestrians also use the interchange. In just one hour there were 6 people walking and 3 people biking on 4th St NW across the interchange. There are currently no cross walks or bike lanes at this interchange. However, there are sidewalks on both sides of 4th St NW.

Conclusion

The movement of most concern observed was I-90 eastbound off-ramp left turn onto northbound 4th St NW (2), because if there were more than two vehicles turning left onto I-90 eastbound on-ramp the vehicles turning left onto 4th St NW northbound could not turn, if there were less than two vehicles turning left onto I-90 eastbound on-ramp than the vehicles turning left onto 4th St NW northbound had to turn behind the vehicles turning left onto I-90. When the vehicles turning left onto 4th St NW northbound turned behind the vehicles turning left onto I-90 it was hard for vehicles going northbound on 4th St NW to see the vehicles turning. Other concerns for the I-90 and 4th St NW interchange are the quick left turn some vehicles had to make to get onto I-90 eastbound on-ramp, the queuing of vehicles behind vehicles turning left onto I-90 westbound on-ramp and vehicles changing quickly to the right lane to avoid the vehicles turning left onto I-90 westbound on-ramp, difficulty turning left for vehicles exiting Burger King, and the absence of cross walks and bike paths.

Burger King