Pennsylvania Route 100

Pennsylvania Route 100 (PA 100) is a 59.4-mile (95.6 km) long state highway in the U.S. state of Pennsylvania that runs from U.S. Route 202 (US 202) near West Chester north to PA 309 in Pleasant Corners. The route runs between the western suburbs of Philadelphia and the Lehigh Valley region of the state, serving Chester, Montgomery, Berks, and Lehigh counties. PA 100 intersects several important highways, including US 30 in Exton, the Pennsylvania Turnpike (I-76) near Lionville, US 422 near Pottstown, US 222 in Trexlertown, and I-78/US 22 in Fogelsville. Several sections of PA 100 are multi-lane divided highway with some interchanges, including between US 202 and the Pennsylvania Turnpike in Chester County between south of Pottstown and New Berlinville, and between Trexlertown and Fogelsville.

PA 100 was originally designated as PA 62 in 1927, running between the Delaware border south of Chadds Ford and US 309/PA 312 in Allentown. PA 62 was rerouted to reach its northern end at PA 29 (now PA 309) in Pleasant Corners a year later. A northern section of PA 62 was designated between PA 15 in Wilkes-Barre and US 106/PA 7 (now US 6) in Tunkhannock in 1927, being replaced with PA 92 a year later. In 1932, PA 62 was renumbered to PA 100 to avoid duplication with US 62. In the 1950s, the route was realigned between south of Bechtelsville and Bally. PA 100 was moved to its four-lane alignment between south of Pottstown and New Berlinville in the 1960s.

Between the 1950s and 1960s, the northern terminus was cut back to Fogelsville with US 309 replacing the route north of there. The section of the route between Exton and Lionville was widened between the 1950s and the 1970s. A freeway along the route in Chester County was proposed in the 1960s, with a short section built between PA 100 south of Exton and US 202 north of West Chester. The southern terminus of PA 100 was moved from Delaware Route 100 (DE 100) at the state line, and placed at the south end of the freeway connector to US 202, in 2003 in order to reduce through traffic in West Chester. PA 100 was rerouted to bypass Trexlertown in 2005. A bypass of Eagle called Graphite Mine Road was completed in 2009, but PA 100 remained on its original alignment after the bypass was built.

PA 100 begins at a partial interchange with the US 202 freeway north of West Chester in West Goshen Township, Chester County, with access to southbound US 202 and from northbound US 202. From this interchange, the route heads northwest as a four-lane freeway past suburban development, crossing the East Branch Chester Creek before heading into West Whiteland Township. PA 100 comes to a southbound exit and northbound entrance with Pottstown Pike, at which point PA 100 becomes part of Pottstown Pike. The road passes under Amtrak's Keystone Corridor railroad line west of the Exton station, which serves Amtrak and SEPTA's Paoli/Thorndale Line trains, and an abandoned railroad line before coming to an interchange with the US 30 freeway, where PA 100 becomes a four-lane arterial road.

Past the US 30 interchange, the route heads north-northwest into Exton as a six-lane arterial road and passes commercial development, running to the east of the Main Street at Exton shopping center. PA 100 crosses US 30 Bus. (Lincoln Highway) and passes to the west of Exton Square Mall. From here, the route continues north as a divided roadway with several intersections controlled by jughandles. The road heads north past more commercial development and narrows to four lanes as it heads into more wooded areas with some development, crossing into Uwchlan Township. PA 100 passes a northbound weigh station before it comes to an intersection with Marchwood Road/Ship Road. The route curves to the northwest and continues near suburban residential and commercial development, turning to the west and intersecting PA 113 in Lionville. PA 100 heads northwest between woods to the southwest and fields to the northeast as it reaches a double trumpet interchange providing access to the Pennsylvania Turnpike (I-76) at the Downingtown interchange. The road passes near business parks and enters Upper Uwchlan Township as it crosses under the Pennsylvania Turnpike and reaches Eagle.

Upon reaching Eagle, PA 100 becomes a five-lane road with a center left-turn lane before it turns northwest to remain on two-lane undivided Pottstown Pike, with Graphite Mine Road continuing straight to bypass Eagle to the east. The route passes businesses in the center of Eagle, where it meets Little Conestoga Road adjacent to the Eagle Tavern and briefly becomes a divided highway. From here, PA 100 heads north as a undivided road and intersects with Graphite Mine Road again. The road continues past a mix of residential subdivisions with some farm fields and businesses. PA 100 crosses into West Vincent Township, where it gains a second northbound lane as it passes through woods. The route becomes a three-lane road with a center left-turn lane as it passes commercial development and comes to an intersection with PA 401 in the village of Ludwigs Corner. Following this, PA 100 becomes a two-lane road and runs through a mix of farmland and woodland, crossing into East Nantmeal Township. The road curves northeast through forested areas and enters South Coventry Township, where it turns north and briefly reenters East Nantmeal Township before continuing back into South Coventry Township. The route continues through rural areas with some development, crossing French Creek and passing through Pughtown before it comes to the PA 23 junction in Bucktown.

After this intersection, PA 100 heads north through wooded areas with some farm fields and residences as a three-lane road with a center turn lane. The road crosses Pigeon Creek into North Coventry Township and passes farm fields before entering commercial areas. The route widens into a divided highway as South Hanover Street splits off to the northeast. At this point, the road becomes a partially controlled access highway with at-grade intersections, some grade separations, and no private driveways. PA 100 turns into a two-lane undivided road and passes over Neiman Road on a bridge as it runs through a mix of rural land and development, widening into a four-lane divided highway. The route comes to an interchange with PA 724 to the west of South Pottstown and to the east of The Shoppes at Coventry. A short distance later, the road reaches a cloverleaf interchange with the US 422 freeway.

Upon crossing River Road and the Schuylkill River on a bridge, PA 100 enters Pottstown in Montgomery County, where it heads through woods and passes over the Schuylkill River Trail and Keystone Boulevard before coming to a bridge over Norfolk Southern's Harrisburg Line. The road reaches a partial interchange with West High Street, with access from northbound PA 100 to westbound West High Street and from eastbound West High Street to southbound PA 100. Immediately after, the route passes west of the Pottsgrove Manor historic house museum and intersects the southern terminus of PA 663, which heads east on West King Street. The road runs past businesses and curves northeast, crossing the Colebrookdale branch operated by the Colebrookdale Railroad at-grade and passing over Manatawny Creek and Manatawny Street. PA 100 runs near residential and commercial development, heading through a corner of West Pottsgrove Township before it enters Upper Pottsgrove Township. The road continues north through wooded areas with some nearby homes and businesses, coming to a bridge over Pine Ford Road before reaching a diamond interchange with Farmington Avenue. The route heads northeast through a mix of farmland and woodland, curving north into Douglass Township. PA 100 heads northeast through rural land with some development and turns north to encounter PA 73 at a diamond interchange in Gilbertsville. Past this interchange, the road continues north near commercial development.