Caterpillar has withdrawn from producing diesel engines for the school bus market, the Forward Advantage will not see production in its current form since its design was tailored to the Caterpillar engine. Hybrid diesel-electric buses IC offers hybrid diesel-electric powertrains in the CE conventional school bus as an option. The buses provide a claimed approximately 40% to 65% better fuel economy but cost about two and a half times more than a standard diesel bus ($210,000 versus $80,000). Enova Systems entered into a long-term supply agreement with IC Bus that guarantees that Enova's proprietary Post Transmission Parallel Hybrid Electric drive system will be used in IC Bus' hybrid electric school buses. The hybrid school bus project features Enova's charge depleting (or "plug-in") or charge-sustaining systems. The drivetrain is powered by Valence Technology lithium ion phosphate battery modules. The braking system utilizes regenerative braking both as a means to reduce wear on the service brakes and to supply the batteries with extra power. Motorcoach prototypes At the 2008 American Public Transportation Association Expo trade show, Navistar announced its intention to enter the intercity motorcoach segment by 2010, unveiling two prototypes produced by IC Bus. Using the MaxxForce 13 powerplant, IC Bus produced a 40-foot-long prototype alongside a 45-foot prototype. Using wind-tunnel design, the company predicted similar fuel efficiency gains that were seen with the streamlined International ProStar semitractor. Following the two prototypes, IC Bus abandoned its efforts in the motorcoach segment, concentrating its commercial buses on school bus derivatives and the HC-Series (a cutaway variant of the International DuraStar). Low Floor IC CE Shorty In 2008, Navistar announced that they would be developing an ICCE Low Floor Shorty School Bus. This involved producing a low floor chassis designed specifically for the CE Shorty. The bus remained the same on the outside in terms of design. It was unknown when production of this bus would start, however due to unknown circumstances, IC Bus abandoned release of the Low Floor IC CE Shorty. The idea of a low floor school bus however, was never completely abandoned, as Collins would introduce their own Low Floor Type A school bus in 2017 built using a RAM low floor chassis. Assembly All IC Corporation/IC Bus vehicles are produced in the Tulsa, Oklahoma, facility opened by AmTran in 1999. Prior to 2008, Type D models were produced in the Ward/AmTran facility in Conway, Arkansas. IC Corporation announced