text: interstate 205 ( california ) interstate 205 ( abbreviated i - 205 ) is a short auxiliary interstate highway that connects interstate 5 with interstate 580 in the san joaquin valley in the u.s. state of california . along with those highways , i - 205 forms the north side of a triangle around the city of tracy . the route provides access from the san francisco bay area to the northern san joaquin valley . it is officially designated as the robert t. monagan freeway after the california legislator who represented the area from 1961 to 1973 . when i - 205 opened in december 1970 , it replaced 11th street , which passed through downtown tracy , as part of the primary all - land connection between the bay area and sacramento until the carquinez bridge opened in 1927 , and carried the lincoln highway and later u.s. route 50 . 11th street is now signed as interstate 205 business . route description interstate 205 begins at the bottom of i - 580 's eight - lane descent from altamont pass into the san joaquin valley . here i - 580 turns southeast to a junction with i - 5 , paralleling the california aqueduct and delta - mendota canal along the foothills , while i - 205 continues east as a six - lane roadway , immediately crossing both waterways . the first interchange is with mountain house parkway , formerly patterson pass road , which serves the planned community of mountain house . next is a split with business 205 , a business loop that follows 11th street through tracy . as i - 205 curves east - northeast and back east through the northern part of tracy , it has interchanges with grant line road ( county route j4 towards antioch ) , tracy boulevard ( county route through downtown tracy ) , and macarthur drive . after several miles without an interchange , the highway ends at a merge with i - 5 , where traffic can continue northeast to the junction with sr 120 near and then east on sr 120 towards yosemite national park or north on i - 5 towards stockton . as it connects to i - 580 , i - 205 is a frequently - congested major commuter route to the bay area . signs on eastbound i - 580 instruct travelers to take i - 205 , sr 120 , and sr 99 to reach modesto instead of using the direct , but non - freeway , route sr 132 . i - 205 also serves to connect the bay area with popular weekend destinations such as yosemite , reno , and lake tahoe . the altamont commuter express provides commuters with an alternate route over altamont pass to san jose and san francisco , the latter through a transfer to bart . history when the department of engineering laid out the initial state highway system after the state 's voters approved a bond issue to pay for it in 1910 , they included route 5 , connecting santa cruz and oakland with stockton via altamont pass . san joaquin county paved the portion near tracy with asphalt with their own bond issue , passed in 1909 , and the state later resurfaced it with concrete . in addition , the new concrete road bypassed banta , which the old county road had passed through via banta road , f street , and grant line road . otherwise , the road was relatively direct , coming down from altamont pass onto grant line road , following byron highway into tracy , and leaving east and northeasterly on 11th street to the san joaquin river at the crossing . the lincoln highway association chose this route in 1913 for their transcontinental highway , where it remained until the carquinez bridge opened in 1927 , creating a shorter route via vallejo . in 1926 , the american association of state highway officials designated the stockton - bay area route as us 48 , which was absorbed by an extension of us 50 by the early 1930s . a 1938 four - lane bypass of the old road around altamont pass was extended east to tracy as a four - lane expressway on november 16 , 1954 . by then , the entire route between the bay area and stockton was four or more lanes , following the present i - 580 ( eastbound lanes where they separate ) , i - 205 , 11th street , and i - 5 from livermore through tracy to stockton . during early planning for the interstate highway system , the main north - south route through california ( now i - 5 ) was to use sr 99 through the san joaquin valley ; a connection to the bay area split near modesto and roughly followed us 50 . the bureau of public roads approved a move to the proposed westside freeway in may 1957 , and in november they added a north tracy bypass that would connect i - 5 and i - 580 . construction began in the late 1960s , incorporating part of the 1954 expressway and a new alignment bypassing tracy to the north , and the $ 14 million road opened to traffic on december 21 , 1970 . ( a short piece at the west end , including the bridge over the california aqueduct , was upgraded several years earlier when i - 580 and i - 5 to the south were built . ) since 1970 , i - 205 has seen few changes . the largest have been widening from four to six lanes west of business 205 in 1999 , and converting two diamond interchanges to partial cloverleafs — grant line road in about 1997 and mountain house parkway in 2007 ( including ramp meters ) . as of summer 2009 , i - 205 has been widened to six lanes ( three in each direction ) for its entire route . also , the 1970s concrete pavement has been resurfaced with fresh asphalt from the junction of i - 5 to due east of the 11th street connector ramp . future caltrans has plans to improve merging distances by constructing auxiliary lanes between the interchanges , and to add new interchanges at lammers road and paradise road . tracy business loop interstate 205 business is a locally maintained business route . it locally follows 11th street , the historic four - lane alignment of u.s. route 50 , through tracy . the route begins at a split with i - 205 west of the city . after passing through downtown tracy , it curves northeast at a junction with former sr 33 , which has been truncated to the south at i - 5 . the final stretch of interstate 205 business runs diagonally to a merge with i - 5 , which comes from the south and continues northeast along the former us 50 alignment . the east end of interstate 205 business is about 3 / 4 mile ( 1 km ) southwest of the end of i - 205 ; normally interstate 205 business would return to i - 205 at both ends , but here i - 205 and interstate 205 business both end at i - 5 . exit list except where prefixed with a letter , postmiles were measured on the road as it was in 1964 , based on the alignment that existed at the time , and do not necessarily reflect current mileage . r reflects a realignment in the route since then , m indicates a second realignment , l refers an overlap due to a correction or change , and t indicates postmiles classified as temporary ( for a full list of prefixes , see the list of postmile definitions ) . segments that remain unconstructed or have been relinquished to local control may be omitted . the numbers reset at county lines ; the start and end postmiles in each county are given in the county column .