So the standard median of that era is about the width of a car? Over here we still build them like that.
No, it wasn't, and actually central reserves in Britain are not normally quite that narrow.
Median widths are measured from edge of traveled way to edge of traveled way (the left shoulder stripe on each carriageway delimits the traveled way). From the mid-1950's onward, the standard median width in many US states was forty feet; Missouri, for example, used this standard when upgrading US 40 to I-70. In Kansas about 80% of the freeway network has been built using a standard width of sixty feet.
Arizona worked to a forty-foot minimum for median width early on, but because most of the rural lengths of Interstate are routed through land which is of very poor value for any agricultural use, much greater median widths were frequently used--I have, for example, plans for parts of I-40 with median widths of 84 feet.
I think the Marsh Station length of I-10 is a special case, forced by the railroad overpass, and probably required a design exception at the time of original construction.
In regard to Britain, typical median ("central reserve") widths vary somewhat but I believe DMRB
still requires that at least two feet be provided on either side of a safety fencing system whose nominal width is two feet, which translates to a six-foot minimum. (DMRB
, of course, expresses these nominal widths in metric units.) Typically, however, provision is more generous than this. The M1 opened in 1959 with a fifteen-foot central reserve. Early in the 1960's there was discussion within the Ministry as to the merits of providing median widths comparable to those used in the USA (such as forty feet), but because land costs in Britain were (and still are) so high, this would have been as expensive as providing two additional paved lanes (one in each direction) while retaining a fifteen-foot central reserve. After some early experiments with glare screening and catenary lighting, safety fences were adopted as the standard solution.