An expert in transportation planning and policy in New Jersey is giving mixed reviews to Gov. Chris Christie’s plan to fund the state’s Transportation Trust Fund.Martin Robins, the director emeritus of the Voorhees Transportation Center at Rutgers University, said it’s there are goof points to Christie’s five-year plan for the trust fund. It provides $200 million for local projects and about $700 million for New Jersey Transit.But Robins said he worries there may not be enough money for the highway network. And he doubts the plan is sustainable.”This is a very shaky thing,” Robins said. “What it does, unlike what a gas tax increase would do, is that this puts us at a cliff at the end of the five years and maybe even before the end of the five years.”Robins said raising the gas tax would have generated long-term revenue for the trust fund. Christie had refused to consider a gas tax increase.