other operating/performance and financial statistics we report key railroad performance measures weekly to the association of american railroads ( aar ) , including carloads , average daily inventory of rail cars on our system , average train speed , and average terminal dwell time .
we provide this data on our website at www.up.com/investors/reports/index.shtml .
operating/performance statistics included in the table below are railroad performance measures reported to the aar : 2008 2007 2006 % (  % ) change 2008 v 2007 % (  % ) change 2007 v 2006 .

<i>2008</i>
<i>2007</i>
<i>2006</i>
<i>% Change 2008 v 2007</i>
<i>% Change 2007 v 2006</i>
Average train speed (miles per hour)
23.5
21.8
21.4
8 %
2 %
Average terminal dwell time (hours)
24.9
25.1
27.2
(1)%
(8)%
Average rail car inventory (thousands)
300.7
309.9
321.6
(3)%
(4)%
Gross ton-miles (billions)
1,020.4
1,052.3
1,072.5
(3)%
(2)%
Revenue ton-miles (billions)
562.6
561.8
565.2
-
(1)%
Operating ratio
77.3
79.3
81.5
2.0 pt
2.2 pt
Employees (average)
48,242
50,089
50,739
(4)%
(1)%
Customer satisfaction index
83
79
72
4 pt
7 pt

average train speed 2013 average train speed is calculated by dividing train miles by hours operated on our main lines between terminals .
ongoing network management initiatives , productivity improvements , and lower volume levels contributed to 8% ( 8 % ) and 2% ( 2 % ) improvements in average train speed in 2008 and 2007 , respectively .
average terminal dwell time 2013 average terminal dwell time is the average time that a rail car spends at our terminals .
lower average terminal dwell time improves asset utilization and service .
average terminal dwell time improved 1% ( 1 % ) and 8% ( 8 % ) in 2008 and 2007 , respectively .
lower volumes combined with initiatives to more timely deliver rail cars to our interchange partners and customers improved dwell time in both periods .
gross and revenue ton-miles 2013 gross ton-miles are calculated by multiplying the weight of loaded and empty freight cars by the number of miles hauled .
revenue ton-miles are calculated by multiplying the weight of freight by the number of tariff miles .
gross ton-miles decreased 3% ( 3 % ) , while revenue ton-miles were flat in 2008 compared to 2007 with commodity mix changes ( notably autos and coal ) explaining the variance in year over year growth between the two metrics .
in 2007 , revenue ton-miles declined 1% ( 1 % ) in relation to the 1% ( 1 % ) reduction in carloadings compared to 2006 .
gross ton-miles decreased 2% ( 2 % ) in 2007 driven by a mix shift in freight shipments .
operating ratio 2013 operating ratio is defined as our operating expenses as a percentage of operating revenue .
our operating ratios improved 2.0 points to 77.3% ( 77.3 % ) in 2008 and 2.2 points to 79.3% ( 79.3 % ) in 2007 .
price increases , fuel cost recoveries , network management initiatives , and improved productivity more than offset the impact of higher fuel prices .
employees 2013 productivity initiatives and lower volumes reduced employee levels throughout the company in 2008 versus 2007 .
fewer train and engine personnel due to improved network productivity and 5% ( 5 % ) lower volume drove the change while productivity initiatives within the support organizations also contributed to a lower full-time equivalent force level .
lower employee levels in 2007 versus 2006 .

Question: Analyse this data from a financial earnings document. based on the operating/performance statistics what was the average operating ratio from 2006 to 2008
Choices:
79.5
239.8
23810
155.6
238.1
Correct choice index: 4