Motorists will be able to travel faster — legally — through three heavily used stretches of interstate in the Baton Rouge area starting Monday.

The Louisiana Department of Transportation and Development announced Friday that the speed limit on portions of Interstate 10 and I-12 will be upped.

The changes are:

I-10 from Essen to Siegen from 60 mph to 65 mph, which is 2.7 miles.

I-12 from Sherwood to Range from 60 mph to 65 mph, which is 5.4 miles.

I-12 from Range to Walker from 60 mph to 70 mph, which is 6.5 miles.

Crews are scheduled to start installing signs on Monday.

“Our study indicated it is reasonable and prudent to adjust the speed limits on these sections of interstate,” DOTD Secretary Sherri LeBas said in a prepared statement.

“DOTD will work with State Police and local law enforcement to closely monitor safety performance and compliance,” LeBas said.

All three sections where speed limits are being raised have been the target of upgrades in recent years, including the addition of one extra lane in each direction. The $341 million, multiyear project, called the Geaux Wider Program, is aimed at improving traffic capacity.

The affected areas also are some of the most heavily used sections of highway in the region, especially during morning and evening rush hours.

Even with the recent improvements, the state Senate is asking DOTD to study the possibility of converting the inside shoulder of I-12 between the I-10/12 split and Walker to a new travel lane to improve traffic flow.

That would mean four lanes in each direction for about 15 miles.

While the announcement was something of a surprise, DOTD officials said traffic engineers launched a study in 2014 to determine the safest and most efficient posted speed limits on I-10 and I-12 after the road improvements.

Rodney Mallett, a spokesman for DOTD, said Friday that after using radar and other checks on newly improved roads, agency officials concluded that now is the time to raise the posted speed limits.

While speed caps are routinely reviewed on state-owned roads, no other similar hikes are in the works for now, Mallett said.

Follow Will Sentell on Twitter, @WillSentell. For more coverage of Louisiana government and politics, follow our Politics blog at http://blogs.the advocate.com/politicsblog/.