The first in a series of increases in Maryland’s gas tax will take place Monday as scheduled — but by not quite as much as had been advertised.

Motorists, who now pay a state gas tax of 23.5 cents per gallon, will see that rise to 27 cents per gallon at the pump on Monday, according to the Comptroller’s Office.

That, of course, is not welcome news for most drivers. But the 3.5-cents increase is less than the 3.8-cents hike forecast by legislative staff when the General Assembly approved a sweeping transportation bill in March. The state Department of Transportation said at the time to expect an initial increase on July 1 of “approximately 4 cents.”

The official calculations that have now been done by the Comptroller have resulted in a less onerous jump.

As a result of the legislation, the existing 23.5-cent tax, which has not changed since 1992, will start being adjusted annually to reflect the Consumer Price Index. That accounts for 0.4 cents of the 3.5-cents increase.

The remaining 3.1-cents rise is the result of a new sales tax that is being applied to gas in Maryland.

Both components will continue to rise in coming years. By mid-2016, motorists can expect to pay between 13 and 20 cents more per gallon than they do now, according to the March estimates by legislative staff.

Before the legislature’s action, transportation officials said they were on the verge of running out of money for new road and transit projects. They now say they have an additional $4.4 billion to spend over the coming six years, including in the heavily congested Washington region.

Last month, as Gov. Martin O’Malley (D) signed the gas-tax increase into law, he released an initial list of $1.2 billion in new spending projects, including $280 million in design work on the Purple Line, the proposed rail link between Bethesda and New Carrollton.

The 1department also is planning to spend an additional $100 million in design work for the Corridor Cities Transitway, a rapid bus line envisioned along Interstate 270. Expanded MARC train service on weekends and several new interchange projects around the state also have been announced. So, too, has a $90 million widening project on a one-mile stretch of the west side of the Baltimore Beltway.