Workers will soon remedy one of Houston's biggest traffic bottlenecks, but not without a few months of pain for drivers - even as one of the region's biggest freeway redesign projects looms over the downtown area.

Starting Friday night, crews will close entrance ramps to southbound Interstate 45 from Houston Avenue, Rusk and Allen Parkway to prepare for rebuilding and redesigning the ramps. As part of the project, estimated to cost $3.6 million, the work also closes the ramp and downtown distribution system that lets traffic transition from the southbound freeway to Dallas, Bagby and Pierce - some of the most common exits for downtown-bound drivers.

"I don't know what I'm going to do," said Michael Flynn, 35, who commutes into downtown from the Heights via Loop 610, I-45 and eventually Dallas.

The exits are expected to reopen in slightly more than two months, depending on weather and construction progress, said Danny Perez, a spokesman for the Texas Department of Transportation's Houston office. New and improved entrance ramps from Houston, Rusk - which some drivers might consider Memorial where the entrance ramp is located - and Allen Parkway are estimated to open in late November.

Based on 2011 traffic counts used during design of the new ramp, 5,800 vehicles use the Allen on-ramp on a typical work day, with another 13,400 merging to the freeway from Houston Avenue. Planners expect use of both ramps in 20 years to have increased by nearly 50 percent.

During the construction, TxDOT and Houston officials said drivers can travel across downtown and access southbound I-45 at Jefferson. The loss of the exits is expected to lead a lot of travelers to exit at McKinney, officials said.

The work removes the current Allen Parkway ramp to southbound I-45, which connects drivers to the freeway on the left side, and replaces it with a ramp aligned with Houston Avenue. The entrance into what is normally the fastest lane of travel creates a situation that " is both unsafe and causes significant traffic congestion," said Lonnie Hoogeboom, director of planning and design for the Houston Downtown Redevelopment Authority. Redevelopment officials are finishing a nearby rebuild of Allen Parkway that adds parking along Buffalo Bayou.

Both the current and upcoming work, however, is dwarfed by a massive total redesign of I-45 from the Sam Houston Tollway south through downtown Houston. Part of that project includes tearing down the segment of I-45 commonly called the Pierce Elevated, just southeast of the upcoming ramp project.

"It is still a number of years out and we want to make these adjustments now," Perez said, explaining why officials would plan a ramp rebuild as they consider wholesale changes. "Something needs to get done, and this is how we are addressing it now."

Cobbling together the estimated $7 billion for the big freeway redesign - including $4 billion for the downtown segment - could take years.

"We have the money now for this to move forward," Perez said.

About $2.2 million of the cost, more than 60 percent of the price, comes from Prop. 1, the voter-approved use of state rainy day funds for transportation projects. Reworking the Allen Parkway ramp was identified as a priority in January 2015, when officials began considering options for the Prop. 1 money.

Other projects have also aimed to solve targeted issues along I-45 as the total makeover looms, Perez said. A new ramp from North Shepherd to northbound I-45 - also redesigned so traffic merged from the slow side of traffic - opened in October.