One ride quality issue PennDOT has made significant progress on is addressing the bump that drivers often encounter when approaching or exiting a bridge.
In typical bridge construction, the roadway must transition from an area supported by compacted but flexible soil embankment layers, known as backfill, to a more rigid bridge abutment support. Due to several factors, including seasonal temperature changes, loss of backfill by erosion, poor drainage, and high traffic loads, the portion of the backfilled roadway can settle over time while the abutment resists settlement. This creates an abrupt elevation change, or "bridge bump," at the transition point. Across the United States, about 25 percent of bridges suffer from bumps at their ends, and state transportation agencies spend an estimated $100 million per year fixing them.
To address this issue, PennDOT has been developing a
Geosynthetic Stabilized Bridge Approach (GSBA) through the State Transportation Innovation Council's Construction and Materials Technical Advisory Group. This innovative approach involves enhancing roadway backfill with layers of geosynthetic material adjacent to a bridge abutment, which significantly reduces pavement settlement.
Typically, roadway backfill is placed in layers, with compaction occurring after each layer. A 2005 Iowa DOT research study demonstrated the effectiveness of enhancing backfill with layers of porous backfill (open-graded aggregate) bound by geosynthetic fabric to minimize the "bridge bump." The fabric and backfill work together to resist the settlement problems encountered with typical backfill, keeping the backfill-supported roadway at the same elevation as the adjacent abutment-supported roadway.
Dennis Neff, P.E., geotechnical engineer in PennDOT's Bureau of Construction and Materials, said a new statewide GSBA construction standard will be in place in 2022.
To date, GSBA has been used successfully on more than 100 bridge approaches in Pennsylvania.
Aside from improved ride quality, GSBA reduces future maintenance costs. PennDOT maintenance forces typically apply asphalt patching or minor grinding to address the "bridge bump." But those remedies do not address the underlying cause. The other maintenance option requires excavation and replacement of the subgrade and pavement, which is costly and requires long-term traffic control setups that inconvenience motorists. GSBA has the potential to reduce maintenance costs by about $3 million a year.