Interstate 170 Missouri


Interstate 170 is the Inner Belt Expressway in the St. Louis metropolitan area. This north-south freeway connects Interstate 270 to Interstate 64/U.S. 40 west of the St. Louis city limits. The Interstate 170 freeway is heavily traveled, servicing suburban cities as a commuter route.


Interstate 170 was originally a part of Missouri 725 when constructed during the 1960s. The route was a part of a planned inner beltway that never made it to full fruition.1 I-170 was established by AASHTO on June 29, 1978 from Interstate 70 / Missouri 725 northward to I-270 over the newly constructed freeway. AASHTO approved the extension of Interstate 170 southward from Missouri 725 to U.S. 40 at Richmond Heights on June 25, 1979.

Originally, Interstate 170 was supposed to continue south into the southern part of St. Louis County. However, by the late 1990s, the neighborhood just to the south voted to kill that plan, as they wanted to keep their community intact. Six months later, MoDOT sold the right-of-way to a developer, which built a shopping center. For more analysis of the southern terminus, we turn to Brian Dowd added:

"...I-170 terminates at a signalized intersection just under I-64/U.S. Route 40. If traffic did not stop, it would run smack dab into a Target...The signal is for traffic on Eager Road.

I-170 has direct connections to both eastbound and westbound I-64/U.S. Route 40 and westbound I-64/U.S. Route 40 has a direct connection to northbound I-170, however there is no direct connection between eastbound I-64/U.S. Route 40 to northbound I-170. Traffic must exit onto Brentwood Boulevard, and can either take Brentwood Blvd south to Eager Rd east to I-170 north or Brentwood Blvd north to Galleria Parkway east to I-170 north, although MoDOT seems to prefer traffic go the northbound route on Brentwood Blvd (that is the route they mark on the Brentwood Blvd exit)."

The northern terminus of Interstate 170 underwent a major redesign project in the early 2000s, and the interchange with Interstate 270 was completed in 2004. Brian Dowd further described the configuration on 09/16/02):

It is still a mystery to me who designed the original interchange at the terminus, but it wasn't exactly intuitive. I-170's junction with I-270 was a directional T interchange, but 3 of the 4 movements were off the left side of I-270. The exit ramp from Westbound I-270 to Southbound I-170 left I-270 from the left lane and the entrance ramp from Northbound I-170 to Westbound I-270 entered I-270 in the left lane. Ok, that makes sense, as these "left" movements at directional T interchanges often enter/exit from the left lane. What didn't make sense is the movement from Northbound I-170 to Eastbound I-270. This logical right movement entered I-270 in the left lane. Ok...let me explain further. The westbound lanes of I-270 were straight on the ground while the eastbound lanes raised upwards and veered slightly to the south at the interchange. The three above mentioned ramps moved under the eastbound lanes (this can be seen from some of the pictures Rich [Piehl] gave you).

This past spring, MoDOT has started a total reconstruction of the interchange. Supposedly some trucker in 1999 or so ended up falling asleep on Westbound I-270 and caused a chain reaction crash that involved a great number of cars in the left deceleration lane to Southbound I-170. After this, residents demanded a change (even though a trucker could fall asleep in the right lane, but that is another story). MoDOT complied and came up with a new design for the interchange which will have all 4 movements entering or exiting I-270 from the right lane and it adds a second lane to the movements that head to/from Illinois. The claim is these changes will double the previous capacity of the very busy interchange. There is a crossover where all 6 lanes of I-270 are currently on what used to be the westbound lanes. MoDOT added a lane plus with the 3 old westbound through lanes and the acceleration ramps from the I-170 ramps, there was enough room to fit in 6 slightly narrow lanes. Along with the interchange modifications, a new I-270 bridge over Hanley Road/Graham Road is being installed with new ramps at the Hanley Road/Graham Road interchange and a slight relocation of Pershall Road (the south outer road).

Currently the only ramp in this interchange that is open is the Eastbound I-270 ramp to Southbound I-170. Traffic wishing to make connections need to detour to surface streets to make their connection, although MoDOT's posted detour is to take I-270 to U.S. Route 67/Lindbergh Blvd to I-70 back to I-170 and vice versa. The interchange modifications are due to be finished by the fall of 2003.

Southern Terminus - Interstate 64/U.S. 40 - Brentwood, Missouri
Perspective from Interstate 170 south
First sign bridge for Interstate 64/U.S. Route 40 on Interstate 170 southbound. Photo taken by Brian Dowd (08/23/02).
Interstate 170 Ends - one mile overhead at Exit 1D/Brentwood Boulevard South. Photo taken by Brian Dowd (06/02).
Three-quarter mile advance sign for Interstate 64/U.S. Route 40. Traffic can be heavy at this terminus in the evening rush hour so this sign alerts drivers of the need to be in the right lane to exit. Photo taken by Brian Dowd (08/23/02).
Fairly close-up view of the Interstate 170 ends 1/2 MILE guide sign posted just above the Galleria Parkway, which leads to one of St. Louis' more known shopping malls, St. Louis Galleria. Photo taken by Brian Dowd (07/12/02).
Rounding the bend to the Interstate 170 terminus. Here traffic is alerted that the left lane is allocated for eastbound Eager Road bound traffic while Interstate 64/U.S. 40 traffic is to utilize the right-hand lane. Just past the cross walk is the exit to westbound Interstate 64/U.S. Route 40. Photo taken by Brian Dowd (07/12/02).
Exit gore for Interstate 64/U.S. 40 Westbound. This area is under construction (2008) for new connections to Interstate 64. Speaking of which, Interstate 64's western terminus is changing as the freeway construction progresses toward Wentzville (where U.S. 40-61 meet Interstate 70). A reassurance shield assembly in St. Charles County between S.R. 94 and the Missouri River lacks a TO banner, and the entrance ramp signage to the westbound Boone Expressway (Interstate 64/U.S. 40/U.S. 61) at S.R. 94 reads WEST I-64/U.S. 40 NORTH U.S. 61/Wentzville. Photo taken by Brian Dowd (06/02).
A different view of the sign at the signalized intersection at the end of Interstate 170. Traffic in the left lane is to turn onto eastbound Eager Road, center lane goes straight into the Brentwood Promenade shopping center, and the center and right lanes turn onto westbound Eager Rd (which ends just to the west of Interstate 170 at Brentwood Blvd). Brian indicates that this intersection is very busy at peek traffic times and estimates that one-half mile back-ups on Interstate 170 can occur. Photo taken by Brian Dowd (06/02).
Perspective from the Brentwood Promenade shopping center
This is taken from the shopping center looking north; Interstate 64 is on the overpass. Photo taken by Rich Piehl (12/00).
This photo is also taken from the shopping center, and it shows the myriad of ramps and streets that MoDOT is going to have to deal with when they rework the interchange. Space is really at a premium here. Photo taken by Rich Piehl (12/00).
Perspective from Interstate 64 west
Approaching the Interstate 170/Brentwood Blvd interchange (they are integrated on Interstate 64/U.S. 40 westbound). This is the first sign of Interstate 170, one mile before the interchange. Photo taken by Brian Dowd (06/29/02).
One half mile before the Interstate 170/Brentwood Blvd interchange on Interstate 64/U.S. 40 westbound. Interstate 170 bears only one control point its entire length. Northbound from Interstate 64/U.S. Route 40 and Southbound from Interstate 70 the St. Louis County Seat of Clayton is used as the control city. No control city is used north and south of Clayton going away from the city. Photo taken by Brian Dowd (06/29/02).
Guide signs on Interstate 64/U.S. 40 eastbound for Exits 31A/B and Interstate 170/Brentwood Boulevard. Photos taken by Brian Dowd (photos #1 and #2 taken 06/29/02, #3 taken 06/02).
Perspective from Interstate 64 east
This panel was slightly changed when the new panels were installed in the past year or so. These centerline panels used to display TO Interstate 170 versus Junction Route Interstate 170 (which by the way is typical fashion for the Missouri DOT to use on these panels now). Maybe this change was done so these panels would not need replacing if the Interstate 64/Interstate 170 interchange is ever rebuilt? Photo taken by Brian Dowd (06/02).
This sign at McKnight Rd actually has the wrong exit number. The interchange for McKnight is actually Exit 30, while Interstate 170/Brentwood Boulevard is designated Exit 31. Photo taken by Brian Dowd (06/02).
The next interchange sequence sign displays Interstate 170 and Brentwood Lane as if they were independent exit ramps. This concept is duplicated on Interstate 165 in Mobile, Alabama, where one interchange serves two different streets. Photo taken 10/16/04.
A more accurate depiction of the Exit number for Interstate 170/Brentwood Boulevard is displayed here. However, it is not completely correct. Brentwood Blvd is actually exit 31A and the absent Interstate 170 exit would be exit 31B. Traffic wanting to access Interstate 170 must utilize the Brentwood Boulevard off-ramp and make at least two turns to reach the freeway. Photo taken 10/16/04.
The transition from eastbound Interstate 64/U.S. 40 to northbound Interstate 170 requires passage through a traffic signal and a good amount of traffic near the mall along Brentwood Boulevard. There is no Interstate to Interstate connection between eastbound Interstate 64 and northbound Interstate 170 - one must use these busy surface streets for a short distance. Photo taken 10/16/04.
If you follow the directions on the overhead you can get on Interstate 170 in about a mile. But if one ignores this sign and turn right here and make two quick lefts, one can get on Interstate 170 in much shorter distance. Whether this route is faster is highly problematic since there is lots of traffic and several stop lights involved. Looking past the stop lights and up the grassy slope is guard rail, which is the ramp from southbound Interstate 170 onto eastbound Interstate 64. This interchange is due to be replaced in the next ten years or so. Photo taken 10/16/04.
This is the shield directing traffic eastbound on Galleria Parkway to access Interstate 170. Making a left at this light will take a motorist to the St. Louis Galleria (one of the larger malls in the St. Louis area). Photo taken 10/16/04.
Perspective from Eager Road
This photo is from Eager Road, which parallels Interstate 64 at this point. Again, lots of ramps and traffic going in lots of different directions. Photo taken by Rich Piehl (12/00).
Three different views of the same signs leading traffic on Eastbound Eager Road to Northbound Interstate 170. The two left lanes of Eager Road Eastbound become the two left lanes of Interstate 170 while the right lane of Westbound Eager Road turning onto Northbound Interstate 170 becomes the right lane of the three-lane freeway. Photos taken by Brian Dowd (06/02).
Northern Terminus - Interstate 270 - Hazelwood, Missouri
Perspective from Interstate 170 north
Northbound Interstate 170 two miles from the terminus at Exits 10A/B. In view are some of the various signs of the upcoming construction that drivers face. No attempts have been made by MoDOT at this point to give notice to motorists warning of the upcoming interchange construction. However it is not as though there was absolutely no sign of the closures as various VMS and construction panels had been erected on Interstate 170 to alert drivers to the construction. Photo taken 10/16/04.
Just past the above sign bridge is this centerline sign 1 3/4 miles south of the terminus at Interstate 270. Photo taken 10/16/04.
How the Interstate 170 northern terminus was originally configured. This scene has drastically changed with construction. The associated sign bridge has also been removed. Photo taken 10/16/04.
Traffic on Northbound Interstate 170 wishing to access Hanley Road must make use of Exit 9C as the connections to Interstate 270 do not allow access from the Interstate 270 ramps to Hanley Road/Graham Rd. This was the case before the interchange reconstruction and will still be the case after the construction is finished. Photo taken 10/16/04.
This Interstate 170 northbound sign bridge is located two miles from the northern terminus with Interstate 270/Exits 10A/B. The left exit for Boeing/Exit 9B essentially dumps one into their parking lot. Photo taken 10/16/04.
As Interstate 170 approaches its northern terminus, the left lane becomes exit only for westbound Interstate 270, while the right lane becomes exit only for eastbound Interstate 270. Use Interstate 270 west to return to Interstate 70 west and Interstate 270 east to Interstate 70 east (and Interstate 55 north). Photo taken 10/16/04.
This photo shows Interstate 170 one-half mile from the northbound terminus. Photo taken 10/16/04.
This photos shows northbound Interstate 170 Ends signage as the freeway approaches Interstate 270. Photo taken 10/16/04.
Northbound Interstate 170 transitions onto westbound Interstate 270 (outer loop) via this ramp. Photo taken 10/16/04.
Perspective from Interstate 270 west
Now traveling west on Interstate 270, this overhead sign is the first indication of the interchange with Interstate 170 south. The next exit is Exit 26B, Hanley Road/Graham Road, followed by Exit 26A, Interstate 170 south. Photo taken by Jeff Morrison (04/19/08).
This mileage sign on Interstate 270 west provides the distance to the New Florissant Road and Hanley/Graham Roads interchanges prior to the revised Interstate 170 interchange. The last of the new ramps connecting Interstate 170 and Interstate 270 opened on November 4, 2003 with a ribbon cutting on the new flyover ramp from westbound Interstate 270 to southbound Interstate 170. The new interchange configuration features all ramps exiting and entering Interstate 270 from the right lane, eliminating all of the former left movements that were at the interchange (including the transition from Interstate 170 northbound to Interstate 270 eastbound ramp that landed into the left lane of Interstate 270). The ramps from westbound Interstate 270 to southbound Interstate 170 and northbound Interstate 170 to eastbound Interstate 270 were built as two-lane movements, but the respective ramps join/leave Interstate 170 as a single lane, either losing/gaining the extra lane in the middle of the ramps. Photo taken by Brian Dowd (01/31/04).
Westbound Interstate 270 reaches Exit 26B, North Hanley Road and Graham Road prior to intersecting Interstate 170, which heads south toward Interstate 70 and Interstate 64. The Interstate 270 bridge over North Hanley Road/Graham Road was rebuilt as a ten-lane bridge from the former eight-lane bridge to accommodate the extra ramp lanes. Through the interchange itself, Interstate 270 shifts slightly to the south of the former alignment between U.S. 67/Lindbergh Blvd and Missouri N/New Florissant Road to accommodate the ramps that connect to/from westbound Interstate 270. Westbound Interstate 270 briefly opens up two auxiliary lanes. The rightmost lane exits off to North Hanley Road/Graham Road to the cities of Hazelwood and Florissant, while the second right lane will exit to Interstate 170 thereafter. Photos taken by Jeff Morrison (04/19/08) and Brian Dowd (01/31/04).
A two-lane ramp connects westbound Interstate 270 with Exit 26A, Interstate 170 south. With construction still in progress when this picture was taken, one of the two exit lanes to southbound Interstate 170 was closed due to the incomplete median wall on southbound Interstate 170. When this was completed a second lane opened up to the right just past the Hanley Rd/Graham Rd exit. The left three lanes, as demonstrated by this large pull-through sign, continue westward on Interstate 270 toward the Interstate 70 interchange in Bridgeton. Interstate 70 ultimately leads traffic to Kansas City (per the control city on the sign). Photos taken by Jeff Morrison (04/19/08) and Brian Dowd (01/31/04).
This view shows the two-lane transition ramp from westbound Interstate 270 to southbound Interstate 170. Past the gore point, the flyover ramp to southbound Interstate 170 gracefully sweeps to the left over Interstate 270. A little more than ten miles to the south, Interstate 170 will reach its southern terminus at Interstate 64/U.S. 40 in Brentwood. Photo taken by Brian Dowd (01/31/04).
Perspective from Interstate 270 west - Prior to Interchange Reconstruction
This series of photos presents the previous configuration of the northern terminus Interstate 170/270 interchange as seen from westbound. One and a half miles before Interstate 170/Exit 26A on Interstate 270 westbound, the exit's former left movement used to be noted by a LEFT LANE advisory where the CLOSED advisory is in this panel. The exit was closed when this picture was taken due to the reconstruction of the northern terminus interchange between spring 2002 and fall 2003. Due to its close proximity to the Interstate 170 interchange, the exit ramps for Graham Road/Hanley Road were also closed for the project to reduce the number of conflict points. Photo taken by Brian Dowd (06/02).
Here are two different views of the centerline exit sign three-quarters of a mile before the Interstate 170 junction. U.S. Route 67/Lindbergh Blvd is a cloverleaf interchange which many motorists go through to access the still open Eastbound Interstate 270 to Southbound Interstate 170 ramp. Under the CLOSED advisory, the old LEFT LANE advisory can be seen as it was left on this sign unlike the one and a half mile sign in which it was removed. Photos taken by Brian Dowd (Top photo 07/07/02; bottom photo 07/12/02).
In this older photo, westbound Interstate 270 approaches Interstate 170 and N Hanley Road/Graham Road - Exits 26A/B pre-construction. As visible with the next photograph, the guide signs on this sign bridge have since been removed. Photo taken by Rich Piehl (11/00).
This picture, at the Hazelwood/Florissant border, gives a really good look at how the interchange used to look. The sign bridge in the background is that at the gore for the former left exit to Interstate 170 Southbound from Interstate 270 Westbound. To the left in view is the way the eastbound lanes, where the white semi truck is driving, used to fly over the ramps to Interstate 170 and the westbound lanes on the ground. The cars above the wall to the right of the westbound lanes are in the old ramp form North Interstate 170 to East Interstate 270 which merged into the left side of Interstate 270. The right panel of the sign bridge is the 3/4 mile advance sign for U.S. Route 67/Lindbergh Blvd. This photo was taken after the Hanley Rd/Graham Rd exit was closed (hence the detour sign on the right side of the photo), but before the Interstate 170 Southbound exit was closed. This area of the freeway currently carries six lanes of traffic by utilizing all of the seen shoulders and some extra additional pavement to the right side of the roadway. Photo taken by Rich Piehl (02/13/02).
Perspective from Interstate 270 east
This view shows Interstate 270 east two miles before Interstate 170 splits and prior to Exits 25A-B Junction for U.S. 67. This sign bridge is just past the entrance ramp from James S. McDonnell Blvd onto Northbound Interstate 270. This is just about where MoDOT considers the direction change of Interstate 270 from North-South to East-West. The associated construction is for the reconstruction of the McDonnell Boulevard interchange, not the Interstate 170 construction that is up ahead. Photos taken by Brian Dowd (06/02 and 08/11/02).
Intertwined with the interchange for U.S. Route 67/Lindbergh Blvd is this sign bridge with the 3/4 mile sign panel for Interstate 170 in Hazelwood. Photo taken by Brian Dowd (08/11/02).
Taken from Pershall Road (the south outer road of Interstate 270), this is the relocation of the 1/4 mile panel for Interstate 170. Just beyond the panel is the interim configuration for the ramp as it was when the construction started. (It has since slightly changed). Photo taken by Brian Dowd (06/02).
Same sign as above with the perspective from Interstate 270. Construction is quite evident in the background. Photo taken by Brian Dowd (06/26/02).
This was the exit from eastbound Interstate 270 onto southbound Interstate 170 in Hazelwood. No control is given although Interstate 170 serves the suburbs of Overland, University City and Brentwood. Since construction has overtaken this junction, the overhead Pictured here has since been removed. Photo taken by Rich Piehl (11/00).


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Page Updated July 30, 2008.