$5.9 million (equivalent to $ in ). If traffic levels were not high enough to raise enough revenue, as the opponents of the project worried, the state would end up paying for the project, thus defeating the purpose of a toll road. The proposed highway was to run from Illinois Route 80 near Port Byron, Illinois, which ran along the eastern bank of the Mississippi River, over a new bridge into Iowa. It would then span across the state to the South Omaha Bridge where US 275 crossed the Missouri River. The entire route was to be in close proximity to US 6 across the state. It was to be the first modern four-lane highway in the state, with lanes and an at least grassy median. Along the route, 16 interchanges were planned. Most interchanges were to be located near population centers; an option to build a 17th near Grinnell, if necessary, was included. Eight service areas, similar in quality to those found on the Pennsylvania and New Jersey turnpikes, were planned as well. On April 29, 1955, an enabling act, which created the Iowa Toll Road Authority, came into effect giving the authority the power to further study the feasibility of building a turnpike across the state. Before any construction was to begin, the authority was tasked with developing working relationships with neighboring states' toll road authorities. A provision in the enabling act prevented Iowa from issuing toll road bonds before neighboring states had issued similar bonds. Plans were stalled while Illinois's toll road commission worked out litigation regarding the financing of its bonds. Illinois was the only neighboring state to have a toll-road-planning body. Construction on the Iowa Turnpike never began. In January 1956, the Federal-Aid Highway Act of 1956 (H.R. 8836) was introduced in Congress. H.R. 8836 created the Interstate Highway System, a national system of controlled-access highways. President Dwight D. Eisenhower signed the bill into law on June 29, 1956. The new law was problematic for the Iowa Turnpike for a couple of reasons. Firstly, the law designated of controlled-access highway in Iowa, including a cross-state route in the vicinity of the turnpike's planned route. Secondly, the federal government was going to pay for 90 percent of the construction costs; states were only required to match 10 percent of costs (however, tolls were generally prohibited). The Interstate Highway System's completeness and financing rendered the Iowa Turnpike