DRAINAGE DISTRICT ASSESSMENTS. 47 
individual tracts because of increased accessibility, an assessment 
should be placed against the road for the same benefit. The cir- 
cumstances in each case will determine whether such a benefit should 
be considered. Such benefits are always somewhat speculative and 
are rarely of large amount. The amount depends on the saving of 
tractive effort and of time in hauling along the effected stretch of 
highway. The ton-mile is theoretically the unit of computation, 
and the amount of benefit depends on the amount and kind of traffic. 
A rough traffic census will give the cost of hauling over the un- 
drained road, which should be compared with the cost on a similar 
stretch of the same type of road drained either artificially or 
naturally. The difference in cost of hauling, multiplied by the ex- 
pected volume of traffic per year, will give the annual saving, and 
this amount capitalized will give the benefit due to increased 
efficiency. 
Care should be taken to value correctly the traffic on a road which 
is avoided and left untraveled because of its undrained condition. 
It is proper to figure the traffic of the drained road at a reasonable 
estimate of what it will be when the drainage work is completed 
rather than what it is at present. The time allowed for prospective 
traffic to develop must however be limited so that no other factors 
than drainage will be responsible for the increased traffic. In some 
cases there is also another element of benefit that should be consid- 
ered under this head, which arises when drainage makes possible the 
construction of a hard-surface road while it is not practicable under 
the undrained conditions. In a district where the road has not yet 
been built the benefit would be the difference in the cost of building 
before and after the construction of the drainage improvement. 
In some cases where tile drains are constructed by the drainage 
district, surface inlets are built at the points where the drain crosses 
the highways, and the cost of these catch basins is added to the high- 
way assessment. This practice is probably fair in Iowa, where bene- 
fits are not assessed but the cost divided among the landowners ; but in 
States where assessments are based upon benefits this practice is un- 
just. If the highway has been assessed for the benefit's of complete 
drainage and surface inlets or catch basins are necessary to give 
complete drainage to the road such an additional charge should not 
be made. 
Whatever the amount decided upon by the board of assessors as 
the benefits due to both the decreased maintenance and increased ef- 
ficiency of the highway, the ratio between the amount of the benefit 
and the amount of the assessment must be the same as in the case of 
farm lands and railroads. 
On the question of building and maintaining highway bridges over 
drainage ditches we find that the laws of various States differ as to 
whether the drainage district or the county shall be responsible for 
the expense. The majority of State drainage laws provide that 
necessary highway bridges shall be built and maintained b}^ the 
drainage district. North Carolina and North Dakota specify that 
while the drainage district shall build the bridges the county or town- 
ship shall maintain them. Illinois, Iowa, Mississippi. Nevada, 
Tennessee, and West Virginia specify that the county shall build 
and maintain the bridges over drainage ditches. There are many 
