From the western suburb of Katy to downtown, I-10 is known as the Katy Freeway in Houston. This section was widened in 2008 to as many as 26 total lanes, counting the six lanes of the access road, which are not limited-access and therefore not technically part of the freeway itself but are directly adjacent.
Between the West Beltway and the West Loop, the minimum lane count is 22 total lanes. In this section, the width is 24 lanes at multiple locations and up to 26 lanes east of Gessner Road (12 main lanes, eight lanes of access roads, and six mid-freeway HOT/HOV lanes). From the Fort Bend county line to I-610, there is a minimum of four main lanes in each direction.
The maximum number of undivided lanes at any point on the freeway is nine in the eastbound direction approaching Antoine Drive (though this includes one exit-only lane); this is one of the widest sections of undivided highway in a single direction in the world. The widest right-of-way, 556 ft (169 m), occurs at the Katy Freeway’s intersection with Bunker Hill; at that point, the expansion plans called for six main lanes plus two toll lanes in each direction along with 10 lanes on the feeder/frontage roads. The actual striping after construction delineates 29 lanes, including all 26 of the planned lanes plus an additional lane in each direction to enter or exit the toll lanes and one more turn lane on the eastbound feeder road.
Between I-610 and I-45 west of downtown, the interstate contains at least five main lanes in each direction. Before 2008, this section had traditionally been the widest section of I-10 in the Houston area and the only one with a significant portion below grade. A project completed in 2014 added one extra auxiliary lane in each direction between Shepherd Drive and Taylor Street. In addition, the eastbound feeder road that ends at Studemont was extended to Taylor Street. As I-10 travels through downtown, it junctions with I-45 and I-69/US 59. Both interchanges feature left exits, allowing several lane shifts for through traffic. I-10 provides access to Minute Maid Park, home of the Houston Astros, and also runs through the campus of the University of Houston–Downtown.
I-10 is the busiest freeway in San Antonio with nearly 200,000 vehicles on an average day. When constructed during the 1960s, the I-10 Katy from Houston, known as the Katy Freeway, was built with six to eight lanes wide barring side lanes, being modest by Houston standards because existing traffic demand to the farming area of West Houston was relatively low. As the population and economic activity increased in the area vehicular traffic increased, numbers of the lanes were increased gradually.