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Traffic heat map of Monroe County, Illinois: 124 miles of roads shaded from blue (light) to red (heavy traffic), busiest on I 255 and IL 3

Monroe County, Illinois Traffic Counts

Its busiest road, I 255, carries 33,013 vehicles a day, 6.8 times the average road. This page breaks down traffic in Monroe County, Illinois across 124 miles of monitored roads split into 2,053 segments, using multi-sourced mobile and sensor data. It goes beyond raw counts to truck flow, congestion and who is driving, so site selection and route planning rest on evidence.
Data sourced from TrafficZoom's proprietary analytics platform.
Data current as of:
Q3 2026
Updated:
September 29, 2026
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Total Traffic Volume & Performance in Monroe County, Illinois

Traffic

The average number of vehicles that travel each day over any road in the road network.

vehicles per day4,877
Trucks

The percentage of the total traffic volume composed of heavy vehicles.

7.0%
Average travel time

The average time of travel averaged among all vehicles traveling on the road network.

29.5 min
Congestion ratio

The rate at which the actual travel time exceeds free-flow travel time, averaged among all roads in the network.

13.0%
Drivers’ average age

Average age of residents in the geographic areas where the vehicle trips originated.

49.2 yrs
Drivers’ average income

Average income of residents in the geographic areas where the vehicle trips originated.

$97,159

Our data shows 4,877 vehicles per day on the average road in Monroe County, Illinois, and 733,965 vehicle-miles traveled per day (≈268 million per year) across its 124 miles of monitored roads. Trucks are a smaller part of the mix than across Illinois: 7.0% against 10.2%.

Shorter trips than 99% of counties in Illinois

Monroe sees 42% lower average daily traffic volume than the state average (4,877 vehicles per day against 8,480), suggesting less demand on each road - less drive-by exposure for retail, but easier access for deliveries. Across the whole network, that travel is about 0.3% of Illinois's statewide total. 77% of counties in Illinois see less traffic than Monroe's 4,877 vehicles per day.

The average trip takes 29.5 minutes, 14% lower than the state level. 99% of counties in Illinois have a longer average travel time than Monroe's 29.5 minutes.

Congestion runs 37% lower than the state level, at a ratio of 13.0%, which means smoother traffic flow - fewer delays make delivery windows more reliable.

Highway vs. Non-Highway Traffic Analysis

highway traffic icon

Highway Traffic in Monroe County, Illinois

Trafficvehicles per day12,654
Trucks7.9%
Average travel time31.3 min
Congestion ratio26.9%
Drivers’ average age48.6 yrs
Drivers’ average income$96,439

Travel in Monroe County, Illinois splits roughly evenly, with about half of it (51% of vehicle-miles) on highways. The average highway carries 12,654 vehicles per day, 180% more than the average non-highway road in the same area, which carries 4,516 vehicles per day.

With 23% of the road miles (29 miles in 91 segments), highways punch above their length, carrying 376,227 vehicle-miles traveled per day (≈137 million per year).

Lower highway truck share than 99% of counties in Illinois

The concentration of trucks on highways (7.9%) is 55% lower than the state average for similar road classifications. Highways here carry mainly commuter and local trips, with little through freight.

Monroe's highway truck share (7.9%) is lower than 99% of counties in Illinois. 70% of counties in Illinois see more highway trucks per day than Monroe's roughly 995.

non-highway traffic icon

Non-highway Traffic in Monroe County, Illinois

Trafficvehicles per day4,516
Trucks6.0%
Average travel time29.4 min
Congestion ratio12.3%
Drivers’ average age49.5 yrs
Drivers’ average income$97,668

Travel in Monroe County, Illinois splits roughly evenly, with about half of it (49% of vehicle-miles) on local roads. A typical local road sees 4,516 vehicles per day.

Spread over 95 miles and 1,962 segments, 77% of the road network, local roads carry a lighter load per mile: 357,738 vehicle-miles traveled per day (≈131 million per year). Trucks make up 6.0% of non-highway traffic, about 1 in 17 vehicles.

Drivers from higher-income areas than 92% of counties in Illinois

Compared to highways, non-highway routes see 24% fewer trucks by share.

At 40% lower than the state level, the non-highway congestion ratio of 12.3% signals easier movement on local roads.

Monroe's average driver income is higher than 92% of counties in Illinois. Monroe's median driver age is lower than 57% of counties in Illinois.

Time-of-Day & Seasonal Patterns

Data Finding: Hourly & Seasonal Patterns

In Monroe County, Illinois, the peak hour concentrates about 7% of the day's traffic.

Monroe County vs. Illinois Traffic Comparison

Monroe County's biggest difference from the Illinois average is its highway truck share, 55% below it. Its average daily traffic per road is also 42% below.

MetricMonroe CountyIllinois averageDifference
Traffic4,8778,480-42.5%
Truck % (Total Traffic)7.0%10.2%-31.6%
Truck % (Highway)7.9%17.3%-54.6%
Avg. Travel Time29.5 min34.1 min-13.6%

How Monroe County compares

Monroe County moves the least traffic of its nearby counties and cities

Compared with its 4 closest neighbours, Monroe County moves 16.4% of the total daily travel and is 31.1% less congested; it has the fourth busiest roads of the five. Less traffic and more room for it - the roads here run both quieter and freer than the areas around them.

Monroe County and the 4 nearest county-level areas by centroid distance, with the Illinois average for scale.
AreaAverage daily trafficTruck shareDaily vehicle-milesAverage travel timeCongestion ratio
Monroe County4,8777.0%733,96529.5 min13.0%
St. Clair County, Illinois7,2629.1%6,124,42131.9 min17.6%
Jefferson County, Missouri6,3297.0%6,507,22730.6 min17.3%
St. Louis City, Missouri9,8257.9%4,407,53934.9 min29.0%
Ste. Genevieve County, Missouri2,75515.8%889,40334.6 min11.5%
Illinois average8,48010.2%N/A34.1 min20.6%

Monroe County ranked within Illinois

Monroe County sits in the bottom quarter of the Illinois field on average travel time, at #101 of 102.

Monroe County ranked among 102 county-level areas in Illinois (1 = highest); measures without data in every county rank a smaller field, down to 82.
MeasureMonroe CountyIllinois rank
Traffic volume (AADT)4,877#24 of 102
Highway vehicle-miles per day376,227#50 of 82
Truck share on highways7.9%#81 of 82
Highway trucks per day995#58 of 82
Average travel time29.5 min#101 of 102
Average driver income$97,159#9 of 102
Average driver age49.2 yrs#59 of 102

The two ends of this table sit far apart: #9 of 102 on average driver income, against #101 of 102 on average travel time.

Busiest roads in Monroe County, Illinois

The three busiest roads in Monroe County average 30,337 vehicles a day, 6.2 times the county average of 4,877 across all its monitored roads.

I 255 is the busiest road, at 33,013 vehicles a day, 2,692 of them trucks (8.2%). IL 3 is practically level with it at 32,564. IL 3 carries the most trucks, 3,293 a day (10.1% of its traffic), although it ranks #2 for all traffic.

Ranked by daily traffic (AADT)

Cars and light vehiclesTrucks
1I 255Motorway · 33,013vehicles2,692trucks · 8.2%
Road class
Motorway
Congestion ratio
26.1%
Median trip time
32.6 min
Drivers’ median age
47.1 yrs
Drivers’ average income
$84,049

I 255 carries 6.8 times the county average on its busiest stretch, where the median trip lasts 32.6 minutes.

2IL 3Motorway · 32,564vehicles3,293trucks · 10.1%
Road class
Motorway
Congestion ratio
42.3%
Median trip time
31.5 min
Drivers’ median age
48.4 yrs
Drivers’ average income
$94,542

Delays build on IL 3: its congestion ratio of 42% over free-flow time is well above the county's 13%.

3Market StreetPrimary road · 25,433vehicles1,181trucks · 4.6%
Road class
Primary road
Congestion ratio
29.9%
Median trip time
30.2 min
Drivers’ median age
48.9 yrs
Drivers’ average income
$99,012

Travel on Market Street's busiest stretch runs 30% over free-flow time, against 13% across the county, so expect slower peak hours.

4Jefferson Barracks BridgeMotorway · 10,755vehicles1,276trucks · 11.9%
Road class
Motorway
Congestion ratio
10.9%
Median trip time
35.1 min
Drivers’ median age
49.3 yrs
Drivers’ average income
$94,443

Jefferson Barracks Bridge carries 2.2 times the county average on its busiest stretch, where the median trip lasts 35.1 minutes.

5IL 158Secondary road · 9,942vehicles385trucks · 3.9%
Road class
Secondary road
Congestion ratio
24.2%
Median trip time
31.7 min
Drivers’ median age
49.1 yrs
Drivers’ average income
$102,439

At 2.0 times the county average, IL 158 draws drivers from neighborhoods averaging $102,439 in household income.

Ranked by trucks per day

Cars and light vehiclesTrucks
1IL 3Motorway · #2 by traffic32,564vehicles3,293trucks · 10.1%
2I 255Motorway · #1 by traffic33,013vehicles2,692trucks · 8.2%
3Jefferson Barracks BridgeMotorway · #4 by traffic10,755vehicles1,276trucks · 11.9%
4Market StreetPrimary road · #3 by traffic25,433vehicles1,181trucks · 4.6%
5Old State Route 3Tertiary road · 3,602vehicles387trucks · 10.8%
Road class
Tertiary road
Congestion ratio
8.4%
Median trip time
33.3 min
Drivers’ median age
47.5 yrs
Drivers’ average income
$99,162

Even at its busiest, Old State Route 3 carries 26% less than the county average; trucks are 10.8% of it, above the county-wide 7.0%.

How to read these road counts
  • The first number is AADT, annual average daily traffic: the vehicles passing a point on an average day, both directions combined and trucks included. On a divided highway both carriageways are added together.
  • Traffic changes along a road, with more near interchanges and towns and less in open country. Every figure for a road describes its busiest stretch in the county, so the two rankings show the same numbers for the same road.
  • The second number is the trucks on that stretch, a part of its AADT. The bar splits the AADT into cars and light vehicles (blue) and trucks (amber).
  • See segment-level AADT for any road on TrafficZoom.

Data Sources & Methodology

The data presented on this page is derived from TrafficZoom's proprietary analytics platform, which aggregates and normalizes information from multiple sources, including:

Mobile device location data (anonymized and aggregated)

Road sensor networks and traffic counters

Historical traffic pattern databases

Public traffic count programs published by the

MonroeDepartment of Transportation

Demographic Baseline for O-D Modeling

U.S. Census Bureau
All metrics represent estimates based on statistical modeling and are intended for strategic planning purposes.
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Data current as of:
Q3 2026

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Counties near Monroe County

The same traffic breakdown for the areas closest to Monroe County, Illinois.

Need segment-level traffic data?

Identify traffic patterns street by street and analyze the exact corridors that matter to your project.