Comparison of Roads.
—In order to compare the relative merits of different types of roads weights are usually given to the different qualities entering into the roadway that they may be compared with a predetermined ideal. It must be remembered that such tables apply only to the particular road for which they are made out. No two can be exactly alike.
Here is one adapted from the author’s work on “Highway Engineering.”[184]
Comparative Table of Several Types of Roadway for Some Particular Locality
| Qualities | Ideal Road for this Particular Location | Best Earth Road | Sand Clay Road | Gravel Road | Mac- adam Road | Brick Road | Con- crete Road | Asphalt Block | Cre- osoted Wood Block | Bitu- minous Con- crete | Sheet Asphalt |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Low first cost | 20 | 20 | 16 | 16 | 15 | 10 | 12 | 10 | 8 | 14 | 13 |
| Low cost of maintenance | 20 | 15 | 15 | 10 | 8 | 9 | 8 | 8 | 10 | 8 | 10 |
| Ease of traction | 10 | 1 | 4 | 6 | 8 | 10 | 10 | 9 | 9 | 9 | 10 |
| Non-slipperiness | 10 | 9 | 9 | 9 | 9 | 8 | 5 | 5 | 5 | 5 | 5 |
| Noiselessness | 5 | 5 | 5 | 5 | 4 | 1 | 1 | 2 | 4 | 2 | 2 |
| Healthfulness | 10 | 5 | 5 | 6 | 8 | 9 | 9 | 9 | 8 | 9 | 9 |
| Freedom from dust and mud | 10 | 1 | 2 | 3 | 4 | 9 | 9 | 9 | 9 | 9 | 9 |
| Comfortable to use | 10 | 3 | 4 | 5 | 6 | 8 | 8 | 9 | 9 | 9 | 9 |
| Appearance | 5 | 2 | 3 | 3 | 4 | 3 | 4 | 5 | 5 | 5 | 5 |
| Total | 100 | 61 | 63 | 63 | 66 | 69 | 66 | 66 | 67 | 70 | 72 |
Tilson gives the following weights for city pavements having heavy traffic:[185]
| Pavement Qualities | Per- cent- age | Gran- ite Block | Wood Block | Brick | Sheet As- phalt | Bitu- lithic |
|---|---|---|---|---|---|---|
| Cheapness | 14 | 8 | 8 | 13 | 14 | 12 |
| Durability | 21 | 21 | 16 | 12 | 15 | 15 |
| Easiness of cleaning | 15 | 10 | 14 | 15 | 14 | 14 |
| Light resistance to traffic | 15 | 13 | 14 | 15 | 11 | 12 |
| Non-slipperiness | 7 | 7 | 4 | 6 | 5 | 6 |
| Ease of maintenance | 10 | 10 | 8 | 6 | 6 | 6 |
| Favorableness to travel | 5 | 2 | 5 | 3 | 4 | 4 |
| Sanitariness | 13 | 9 | 13 | 10 | 12 | 12 |
| Total | 100 | 80 | 82 | 80 | 81 | 81 |
| Less cheapness | 72 | 74 | 67 | 67 | 69 |
The Forest Service of the U. S. Department of Agriculture presents the following table:
| Pavement Qualities | Per- centage | Granite Block | Sheet Asphalt | Brick | Mac- adam | Wood Block | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Cheapness | 14 | 4 | 6 | 1⁄2 | 7 | 14 | 4 | 1⁄2 | |||
| Durability | 20 | 20 | 10 | 12 | 1⁄2 | 6 | 14 | ||||
| Ease of maintenance | 10 | 9 | 1⁄2 | 7 | 1⁄2 | 8 | 1⁄2 | 4 | 1⁄2 | 9 | 1⁄2 |
| Ease of cleaning | 14 | 10 | 14 | 12 | 1⁄2 | 6 | 14 | ||||
| Low resistance to traffic | 14 | 8 | 1⁄2 | 14 | 12 | 1⁄2 | 8 | 14 | |||
| Non-slipperiness | 7 | 5 | 1⁄2 | 3 | 1⁄2 | 5 | 1⁄2 | 6 | 1⁄2 | 4 | |
| Favorableness to travel | 4 | 2 | 1⁄2 | 4 | 3 | 3 | 3 | 1⁄2 | |||
| Acceptability | 4 | 2 | 3 | 1⁄2 | 2 | 1⁄2 | 2 | 1⁄2 | 4 | ||
| Sanitary qualities | 13 | 9 | 13 | 10 | 1⁄2 | 4 | 1⁄2 | 12 | 1⁄2 | ||
| 100 | 71 | 76 | 74 | 1⁄2 | 55 | 80 | |||||
Crosby gives three sets of ideal crusts for country roads: V for main roads, carrying a fairly heavy mixed traffic, W, secondary roads carrying moderate traffic, and X on minor roads with light farm travel almost wholly.[186]
| Components | Ideal | Brick | Plain Cement Con- crete | Bitumi- nous Mac- adam | Water- bound Mac- adam | ||
|---|---|---|---|---|---|---|---|
| V | W | X | |||||
| First cost, cheapness | 15 | 15 | 15 | 8 | 10 | 10 | 15 |
| Maintenance, cheapness | 25 | 25 | 20 | 25 | 20 | 20 | 10 |
| Durability | 7 | 7 | 7 | 7 | 5 | 5 | 3 |
| Ease of maintenance | 8 | 10 | 10 | 7 | 8 | 8 | 10 |
| Cleanliness | 5 | 5 | 5 | 3 | 3 | 5 | 2 |
| Low tractive resistance | 10 | 5 | 5 | 5 | 4 | 4 | 4 |
| Non-slipperiness | 10 | 10 | 10 | 4 | 7 | 5 | 10 |
| Sanitariness | 5 | 5 | 5 | 4 | 4 | 5 | 3 |
| Noiselessness | 5 | 5 | 5 | 3 | 3 | 5 | 4 |
| Acceptability | 5 | 5 | 8 | 2 | 3 | 4 | 5 |
| Favorableness to travel | 5 | 8 | 10 | 3 | 5 | 6 | 8 |
| Total | 100 | 100 | 100 | 71 | 72 | 77 | 74 |
Anderson gives the following economical table to assist in arriving at a proper type of surfacing:[187]
Method of Making Economical Comparison of Road Surfaces
| Item | Possible Types of Surfacing | ||
|---|---|---|---|
| A | B | C | |
| Estimated life of surface with proper maintenance, years | 4 | 8 | 12 |
| Original construction cost per mile | $ 8,000 | $15,000 | $30,000 |
| Annual charges for interest, depreciation and resurfacing | 2,364 | 2,528 | 3,797 |
| Cost of maintaining surface per mile, average, annual | 1,000 | 750 | 200 |
| Total cost per mile at end of 12th year, period | 40,368 | 39,336 | 47,964 |
| Value of road surface per mile at end of 12th year period | .... | 7,500 | 12,000 |
| Net outlay per mile of road | 40,368 | 32,836 | 35,964 |
The choice of selection here is evidently between B and C, with the figures so close together that the one with the least number of uncertainties would probably be adopted if economy is the determining factor.
Another method of making economical comparisons is shown in the table and plot following:
| Item | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Earth Road | Gravel Road | Bitumi- nous Macadam and concrete | Portland Cement Concrete | Sheet Asphalt Bitulithic | Brick Stone Block | Wood Block | |
| First cost per mile | $1,000 | $5,000 | $10,000 | $20,000 | $30,000 | $40,000 | $50,000 |
| Annual Interest, 5 per cent | 50 | 250 | 500 | 1,000 | 1,500 | 2,000 | 2,500 |
| Annual Maintenance | 250 | 250 | 500 | 100 | 100 | 50 | 50 |
| Life of surface, yrs. | 0 | 5 | 10 | 20 | 20 | 25 | 25 |
| Cost of resurfacing | $ 0 | $2,500 | $ 5,000 | $15,000 | $15,000 | $25,000 | $35,000 |
| Annual Sinking Fund 31⁄2 per cent | 0 | 466 | 427 | 530 | 530 | 884 | 899 |
| Annual Total Cost | 300 | 966 | 1,427 | 1,630 | 2,130 | 2,934 | 3,449 |
| Daily Cost, per mile | 0.82 | 2.74 | 3.90 | 4.45 | 5.84 | 8.03 | 9.46 |
Plot showing cost of several types of roads under varying traffic density. When the traffic density of road No. 1 (Earth and sand clay) becomes greater than 300 or 400 vehicles per day the curve would turn up because the maintenance costs would be increased. Similarly for Nos. 2 and 3 for 1600 to 2000 vehicles per day.