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I-480/I-71 INTERCHANGE
In September 1996, NOACA completed a report for ODOT 12 entitled "Freeway Bottleneck Study". A bottleneck
is a major inhibitor to free-flowing traffic and occurs when the flow into a section of freeway exceeds that section's
capacity. The Freeway Bottleneck Study:
- Examined the operational characteristics of freeway bottlenecks for both existing and 2020 traffic
conditions during the morning and afternoon peaks;
- Examined the effect of increasing roadway capacity as a solution to existing and future problems on
selected segments experiencing bottleneck conditions during peak hours; and
- Estimated the traffic reduction needed to reduce peak period congestion to acceptable conditions and
the effects on the bottleneck and its upstream and downstream connections.
The study used the following standards when evaluating each bottleneck:
- The ideal capacity per lane on a four-lane freeway such as I-71 is 2,200 passenger cars per hour;
- The ideal capacity per lane on a six-lane freeway is 2,300 passenger cars per hour; and
- Level of Service D or better is acceptable.
The study findings (Table 3-11) included:
- An unacceptable LOS at I-480/I-71 occurred during the morning and afternoon peaks and that this
condition would prevail to 2020.
- The I-480/I-71 bottleneck was rated the worst freeway bottleneck in the NOACA region based on
existing traffic, with fifty-six (56) accidents occurring within one-quarter mile. This is 60% higher than the next
highest accident. NOACA estimates that these operating conditions will continue until 2020.
- In order to improve the LOS at the I-480/I-71 bottleneck, the number of vehicles per hour would have
to be reduced by 2,400. This could be achieved by adding one lane in each direction at the bottleneck sections to
improve the capacity and reduce the flow rate. However, in 2020, the upstream and downstream segments of the
bottleneck will again have congestion even though the bottleneck level of congestion will be acceptable.
Table 3-11
Level of Service of I-480/I-71 Interchange |
| Direction |
LOS at Peak Periods
Existing Traffic |
LOS at Peak Periods
2020 Traffic |
| AM |
PM |
AM |
PM |
| Northbound |
E |
B |
F |
B |
| Southbound |
D |
F |
D |
F |
| LOS Acceptable -- LOS Unacceptable |
| SOURCE: NOACA Freeway Bottleneck Study, September 1996 |
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