NEW PORT RICHEY –— The cost of a diamond is getting pricier.The planned "divergent diamond" interchange, intended to ease traffic congestion at Interstate 75 and State Road 56 where Lutz, Land O’Lakes and Wesley Chapel intersect, is going to be more expensive than originally projected.So expensive that the local transportation planning board had to hold a public hearing to amend its adopted spending plan — a requirement whenever project costs go up by 20 percent.In this case, it was a lot more. The construction cost nearly doubled from $21.1 million to $40.2 million, according to the public hearing notice of the Pasco Metropolitan Planning Organization, made up of county commissioners and elected city officials.Kris Carson, regional spokesperson for the state Department of Transportation, said the price has declined a little since. As design work progressed, the construction cost dropped and now is estimated at $37.4 million, she said via e-mail.Even so, the higher costs "really took us back,’’ said Kelly Miller, chairman of the citizens committee that advises the transportation board. The DOT briefed the citizens panel on the rising prices Jan. 28.MPO members, however, appeared non-plussed. At the Feb. 22 hearing, they voted unanimously to amend the transportation plan to include the higher spending without asking if anyone from the public was there to comment.It apparently didn’t matter. Nobody was.But the lack of a public vetting by the MPO didn’t go unnoticed."I’m surprised nobody questioned that. Why would you not question that?’’ Christie Zimmer, a member of the citizens committee, asked afterward.The price escalated because the state had to revise the length and width of the earth retaining walls, traffic rails and guardrails, plus it redesigned the paving and plans to add a permanent sheet pile wall and high-mast lighting, the public hearing notice stated.At the MPO hearing, however, the only questions focused on the construction time line.Bill Jones, DOT’s regional development director, said construction bids are scheduled to be opened in June, with work likely to begin in the late summer or early fall. The project is expected to be completed in 26 months.Carson said the higher costs will be covered by a statewide contingency reserve account and will not delay other DOT work planned for Pasco County."In the zero sum game, that is transportation funding. That $16 million will not be available for another project, but woo, we get ours,’’ said Craig Casper, the MPO transportation planning manager.The divergent diamond is so named because it diverts traffic patterns associated with the traditional diamond-shaped highway interchange. In this case, the interchange will eliminate waits for left-hand turns by motorists entering I-75. The new east-west traffic pattern on SR 56 will divert vehicles to left lanes for a short distance. Then they either enter the interstate without pause or continue as through traffic by returning to right lanes.The rebuilt interchange is expected to ease the bottleneck in the fast-growing area where rush-hour traffic routinely backs up on I-75’s northbound exit lane to SR 56. Demand for the improvement was so great that DOT moved up its construction schedule by six years to begin the work in 2018.Reach C.T. Bowen at [email protected] or (813) 435-7306. Follow @CTBowen2RELATED: DOT advances interchange project.