One out of three motorists who uses the Intercounty Connector without an E-ZPass transponder doesn’t pay the toll bill sent by mail. (Mark Gail/The Washington Post)

Nearly one in three motorists who use the Intercounty Connector without an E-ZPass transponder don’t pay the toll later, making Maryland’s newest and most expensive highway home to a toll violation rate four times higher than the state average.

Individual motorists racked up as much as $1,418 each in unpaid tolls after driving on the ICC, or Route 200, as many as 430 times during the first six months of this year. A rental car company owed $4,263 in ICC toll debt, while a construction company accrued $2,241 for 65 unpaid trips during that time.

The new 18.8-mile highway between Gaithersburg and Laurel has added quickly — and relatively significantly — to the state’s toll losses. The ICC accounts for 5 percent of the state’s toll revenue. However, the nearly $670,000 in unpaid tolls between January and June amounted to almost 30 percent of all tolls that went uncollected statewide during that time, according to figures obtained from the Maryland Transportation Authority.

The ICC’s problem is twofold: As an all-electronic road with no toll booths, the ICC can charge tolls only by deducting them from E-ZPass transponders or by mailing a photo of the vehicle tag along with an invoice for a higher “video toll” to the vehicle’s registered owner. However, Maryland’s tolling authority doesn’t use the kinds of enforcement measures — vehicle registration suspensions and court referrals — that tolling experts say are the most effective in getting people to pay the mailed bills.

State Sen. Catherine E. Pugh (D-Baltimore), chairman of the Senate Finance Committee’s transportation subcommittee, said she plans to hold a hearing early next year on the state’s toll collection methods.

“We can’t afford to leave money on the table,” Pugh said. “The ICC was a very expensive road to build.”

As the ICC on Thursday marks the first anniversary of its full opening, its violation rate is noteworthy because it is the Washington region’s first all-electronic toll road. Made possible by new technology, all-electronic tolling is gaining popularity across the country as a way to move traffic, reduce vehicle emissions and improve safety.

Maryland officials are considering all-electronic systems for the state’s seven other toll facilities, and the tolled express lanes under construction on Interstate 95 northeast of Baltimore will be all-electronic. The new tolled express lanes that opened Saturday on the Virginia side of the Capital Beltway also have no toll booths.

Meanwhile, motorists who do follow the rules on the ICC are paying some of the highest toll rates in the country, and toll-payers throughout Maryland are subsidizing whatever ICC motorists don’t cover to pay off the road’s construction costs. The authority recently raised tolls statewide to cover construction financing costs on the $2.56 billion ICC and the $1 billion express lanes on I-95. Tolls are scheduled to increase statewide again in July, in some cases more than doubling since October 2011.

Harold Bartlett, the authority’s executive secretary, said he is “using every arrow in my quiver” to enforce toll collections by mail but said the ICC’s overall violation rate of 2.8 percent did not significantly affect the authority’s financial health. Statewide, the authority collects all but about 0.67 percent of tolls, he said.

“I don’t want to minimize anything because every dollar is important to collect, but if you did an audit . . . this does not have a ‘material impact,’ ” Bartlett said.

Even so, with ICC traffic anticipated to grow significantly — and, with it, the potential for toll cheating — the authority has proposed legislation that would impose a $50 civil citation for any video tolls not paid within 30 days.

Current state law requires a $50 civil citation immediately upon not paying at a toll booth. Instead, the authority imposes a $25 fee only after 30 days to allow vehicles to use E-ZPass lanes and the ICC without a transponder. Current law also allows the state to go after the vehicle registrations of chronic toll cheats. However, the Maryland Motor Vehicle Administration hasn’t done so in more than two years, citing the fact that the authority’s $25 fee doesn’t follow state law. That has left the authority sending chronic violators a series of letters requesting payment.

The legislation proposed by the authority would allow the state to resume suspending vehicle registrations and flagging others for nonrenewal until tolls are paid and publicize the names of the worst scofflaws in a “Hall of Shame.”

Maryland’s other toll facilities will not be converted to all-electronic tolling until the authority has stiffer penalties for those who refuse to pay by mail, Bartlett said.

“I won’t make us vulnerable to that weakness until I have a way to go after them,” Bartlett said.

The ICC’s violation rate highlights the potentially mounting costs from Maryland’s relatively lax tolling enforcement. As The Washington Post reported in September, Maryland had done little compared with other states over the past five years to collect $6.7 million in unpaid tolls statewide from nearly 650,000 vehicle owners who had used E-ZPass lanes without a transponder.

After The Post highlighted the problem, the state began reporting toll violators to credit agencies and secured payment from a car rental company that had one of the biggest debts, Maryland officials said.

ICC motorists without an E-ZPass transponder are paying the mailed toll bills more frequently than those using other Maryland toll facilities. Statewide, 37 percent of those billed by mail didn’t pay within the 30 days, compared with 30 percent who had driven the ICC, according to the authority.

However, the effects are more acute on the ICC because about 10 percent of motorists use it without a transponder. At other Maryland toll facilities, where people without transponders can still pay at toll booths, about 2 percent are billed by mail.

Several national tolling experts said a 30 percent violation rate for vehicles without transponders was fairly typical for all-electronic toll roads but could be reduced with tougher enforcement.

Greg Le Frois, a consultant in toll technology and operations for Kansas City-based HNTB, said a toll road like the ICC, which carries primarily local traffic, could get that down to 15 or 20 percent with tougher penalties for ignoring the mailed invoices. He said some tolls go uncollected because addresses on vehicle registrations are outdated or out of state.

“If that amount of uncollectibles starts to creep up or they get a reputation for not collecting, people think, ‘I’m going to violate until you come and get me,’ ” Le Frois said.

To keep violations in check, experts said, agencies often seek stiffer penalties for chronic violators before instituting all-electronic tolling. In Virginia, for example, vehicle owners with three or more unpaid toll violations face a maximum $500 civil penalty. However, motorists who use the new all-electronic Beltway express lanes without a transponder and ignore the mailed bill face up to a $1,000 fine.

Megan DiGiovanni, 25, said she dutifully pays the invoices she receives by mail when her E-ZPass account runs low and the transponder doesn’t register on the ICC. She said she spends about $160 per month — $8 daily — on ICC tolls because the free-flowing toll road cuts up to 50 minutes each way off her commute between Rockville and her sign-language interpreter job in Baltimore.

Upon hearing that one-third of motorists without E-ZPass are skipping out on ICC tolls, DiGiovanni said, “That drives me crazy . . . because I make an effort to pay.”

State Comptroller Peter Franchot said the authority needs to step up its collection efforts, such as by taking chronic violators to court, before waiting for stiffer legislation.

“Why would you pay a toothless tiger?” Franchot said. “Obviously, word is going out that Maryland is taking the ‘free state’ to a new level.”