Illinois Department of Transportation, Erica Borggren, Acting Secretary
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Purpose and Need

The purpose of the U.S. 20 project is to improve:

  • the capacity of the joint segment of I-39 and U.S. 20,
  • the I-39 and U.S. 20 interchange, and
  • the I-39 and U.S. 20/Harrison Avenue interchange.

The project will also improve lane balance and simplify traffic maintenance during future construction projects by providing two lanes in each direction on I-39 through the I-39 and U.S. 20 interchange. I-39 through traffic is restricted to one lane in each direction at the I-39/U.S.20 interchange. I-39 through traffic also goes through standard exit and entrance ramp terminals. Both of these items are contrary to current design policy.

The need for the U.S. 20 improvement project is described below in several sections, including Conditions of the Existing Highway Network, Existing Traffic and Capacity Deficiencies, Crash Information, and Alignment and Profile Deficiencies.

Conditions of the Existing Highway Network

U.S. 20 is a marked federal highway and is part of the national highway system.

Most of U.S. 20 and I-39 in this project area was constructed in the early 1960s and is now part of the federal interstate and national highway system. I-39 is a four-lane divided highway with 24-foot wide pavement in each direction separated by a 40-foot grass median. The inside shoulders are paved an additional 4 feet, and the outside shoulders are paved an additional 10-feet. Drainage is provided in roadside ditches. The existing pavement consists of 10-inch thick concrete with a 3-inch asphalt overlay.

The I-39 and U.S. 20 interchange was constructed in the 1980's and is a three-legged, non-standard design. Through traffic on I-39 goes through exit ramps and is reduced to one lane in each direction.

The I-39 and U.S. 20/Harrison Avenue interchange is a standard cloverleaf design. The loop ramps at the interchange have very tight curves. Vehicles entering and exiting must cross each other in the very short distance between the exit ramp and the entrance ramp. This traffic conflict is called "weaving." Eliminating this weaving can significantly improve interchange safety and operations.

I-39 is a full access-controlled freeway, which means that motorists may only enter or exit at interchanges. U.S. 20 west of I-39 is also full access-controlled within the project limits. The first point of access on U.S. 20/Harrison Avenue to the west of I-39 is South Mall Drive, and to the east of I-39 is Mill Road. Each point of access is located approximately 2,000 feet from I-39. There is no access control on Harrison Avenue west of Perryville Road. East of Mill Road, U.S. 20 is a partial access-controlled expressway with median crossovers at approximately one-quarter mile intervals.

None of the other roadways in the project limits have access control except at the I-39 grade separations.

Existing Traffic and Capacity Deficiencies

IDOT District 2 determined the projected construction year traffic (2015) and design year traffic (2035). These projections are shown in Table 1.

Table 1. Projected Traffic

 
Average Daily Traffic (ADT)
 
2015
2035
I-39 South of U.S. 20 37,500 61,600
I-39/U.S. 20 63,800 104,800
I-39 North of U.S. 20 47,200 77,700
Harrison Avenue West of I-39 29,100 47,950
Harrison Avenue East of I-39 34,200 57,100

The I-39 mainline has surpassed its current traffic capacity, and motorists experience traffic congestion. The severity of this congestion warrants additional lanes.

Crash Information

A review of accident history was conducted for the study area of U.S. 20 and I-39 for the years 2002, 2003 and 2004.

A further breakdown by mile stationing reveals that there are some segments experiencing a significant number of accidents. Table 2 illustrates the number and percent of total accidents, for various types, that have occurred in the study area.

Table 2. Number and Percent of Total Accidents in
Study Area IL-39 Mile Station 117.19-122.51 during 2002-2004

Collision Type Overturn Rear-End Fixed Object Animal Sideswipe Other TOTALS
No. of Accidents 13 51 49 34 36 27 210
% of Total Accidents 6% 24% 23% 16% 17% 13% 100%
  • There were forty (40) fixed object accidents occurring between miles 118.50 and 122.75, with six near the piers and abutments at the overhead bridge for Harrison Avenue.
  • Thirty-seven (37) rear-end accidents have occurred between miles 120.75 and 123.00. Specifically, miles 122.50 to 122.75 contain ten rear-end accidents, five in the eastbound direction and five in the westbound direction. This is possibly due to sudden stops when trying to merge into traffic on I-90 or as a result of sudden reductions in speed when entering onto ramps.
  • Four (4) overturn accidents have occurred in the 0.25 miles stretch where IL-39 connects with I-90. Vehicles traveling at excessive speeds adjacent to steep embankment slopes are the likely source of these accidents.
  • Miles 119.00 to 122.00 have produced twenty-one (21) animal collision types, which may be reduced if an improved fence is placed in this segment to deter animal crossings.
  • Seven (7) sideswipe collisions have occurred in the quarter-mile stretch from 119.50 to 119.75, most likely from the merging traffic of U.S. 20 and IL-39. These collisions take place in the segment where southbound vehicles are decelerating to exit on to the ramp as well as where northbound vehicles are trying to merge with the eastbound traffic of U.S. 20.

Table 4 shows a summary of the total number of accidents that have occurred under various conditions. These totals are based on all roads in the given study area. In general, 127 accidents (60.5%) occurred on dry surface conditions, 147 accidents (70.0%) in clear weather conditions, and 144 accidents (68.5%) in daylight conditions. This data shows that the majority of the accidents took place during daylight hours when surface conditions were dry and the weather was clear

Table 4. Number of Accidents Occurring Under Various Conditions
in the Study Area during 2002-2004

Surface Conditions
 
Dry
Wet
Ice
Snow
Unknown
No. of Accidents
127
39
3
29
12
Weather Conditions
 
Clear
Rain
Snow
Other
No. of Accidents
147
31
27
5
Lighting Condition
 
Daylight
Night
Dawn
Dusk
No. of Accidents
144
55
6
5
Direction of Cars
 
North
South
East
West
Opposite
No. of Accidents
51
26
72
56
5

Alignment and Profile Deficiencies

Several aspects of the current U.S. 20 project area are deemed deficient by current policies and standards.

I-39/U.S. 20 Interchange
I-39 through traffic is restricted to one lane in each direction at the I-39/U.S. 20 Interchange. I-39 through traffic also goes through standard exit and entrance ramp terminals. Both of these aspects are contrary to the current policy.

The curve radii on I-39 through the interchange are 1161 feet and 1145 feet, and this is less than the 1,205-foot minimum allowed to remain in place for a 60 mph design speed.

A lower curve radii figure means that the curve is tighter, which will require motorists to reduce speeds throughout the curve.  The required radii for a 60 mph curve is a more gradual curve than either of the current curve designs. The more gradual curve is a safer design and will also help traffic flow quickly through the curve.

I-39/Harrison Avenue Interchange
Loop ramps at the Harrison Avenue/I-39 Interchange have radii smaller than the required minimum. The northbound to westbound and southbound to eastbound ramps have a minimum radius of 185 feet. The minimum design speed of 30 mph requires a radius of 250 feet. The eastbound to northbound and westbound to southbound loop ramps have a radius at Harrison Avenue of 230 feet and a radius of 310 feet at I-39.

Vertical curve, which is the curve level when traveling over non-flat areas, is graded on sight distance. The vertical curve on eastbound U.S. 20 to southbound I-39 Station 55+90 has a poor sight distance for a design speed of 50 mph, and this sight distance is below the required sight distance level. By increasing the sight distance, these vertical curves will be safer for motorists.

I-39/U.S. 20 Improvement Project

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