Road Pavement Useful Life

Methodology for Estimating Asset Life from Consecutive Condition Assessments

Table 1

The table below shows example (made up) PCI data for road segments re-inspected after 5 years.

Year 0 Condition	Year 5 Condition	Average Condition	Annual Rate of Change
15	30	22.5	3
25	55	40	6
33	51	42	3.6
45	75	60	6
48	79	63.5	6.2
56	100	78	8.8
58	98	78	8
66	90	78	4.8
75	85	80	2
82	102	92	4
85	112	98.5	5.4
89	122	105.5	6.6
91	132	111.5	8.2
95	115	105	4
101	129	115	5.6
110	139	124.5	5.8
115	133	124	3.6
120	171	145.5	10.2
121	155	138	6.8
125	156	140.5	6.2
128	165	146.5	7.4
129	150	139.5	4.2
135	170	152.5	7
139	175	157	7.2
141	166	153.5	5
150	220	185	14
160	5	82.5	-31
175	6	90.5	-33.8

The last two points are meant to represent roads that have been reconstructed in between inspections are excluded from the analysis. The remaining points are graphed below.

A quick bit of high school math

Rate of Change of Condition = A * PCI Score + B

You could do a least mean squares fit if you want to, but for this example I have just picked a line by eye.
(It would be nice if real data follows an obvious pattern, but I suspect real data will be equally scattered).

The red line runs through the points (0,2) & (157,7.2)

Which gives the equations:
2 = A * 0 + B - (1)
7.2 = A * 157 + B - (2)

Therefore B = 2 and A = (7.2-2)/157 = 0.033121019

Which gives the equation: Rate of Change of Condition = 0.033121019 * PCI Score + 2

It follows that : PCI (year n+1) = PCI (year n)*1.03312019 + 2

This yields the following graph

And the above graph not only gives you a way of semi-scientifically determining a useful life for road pavements, it also lets you estimate the expected remaining useful life of any road segment you have a condition score for.

Depending on your scoring system and construction standards an assets initial condition may not be zero.

If for example a typical road has a PCI of 10 immediately after construction, and you have adopted a service level that roads should be reconstructed when the PCI is greater than 200, a typical road would have a useful life of 40 years.