The following appeared in a letter to the editor of a local newspaper.
"Commuters complain that increased rush-hour traffic on Blue Highway between the suburbs and the city center has doubled their commuting time. The favored proposal of the motorists' lobby is to widen the highway, adding an additional lane of traffic. But last year's addition of a lane to the nearby Green Highway was followed by a worsening of traffic jams on it. A better alternative is to add a bicycle lane to Blue Highway. Many area residents are keen bicyclists. A bicycle lane would encourage them to use bicycles to commute, and so would reduce rush-hour traffic rather than fostering an increase."
Write a response in which you discuss what specific evidence is needed to evaluate the argument and explain how the evidence would weaken or strengthen the argument.
According to the editorial, the author concludes that the Blue Highway (BH) should have a bike lane added to solve the traffic problem during peak hours. To support this conclusion, the author points out that people complain about the long commute times during the rush hour, and that the addition of a lane on the Green Highway (GH) exacerbates the problem, and that many residents prefer to ride bicycles. Hence, the best way to solve the congestion on the BH is to add a bike lane. Although the author's arguments seem reasonable, much evidence is needed to further evaluate this conclusion.
First, we need to know the representativeness of local commuters' complaints. In the editorial, the author concludes that BH needs to address traffic issues by citing commuters' complaints. However, the author does not provide enough information to support the credibility of these complaints. For example, there may be few people who actually complained. It is also possible that those who do complain have changed the commute times so that everyone's commute is at peak traffic times. It is also likely that the commute time doubled but had little impact (e.g., from 5 to 10 minutes), or that the severity of the problem was exaggerated for the sake of attention. If there is evidence of any of these, then the credibility of the complaints cited by the author is undermined, and the author's conclusions are overturned. However, if there is evidence that people's complaints are widespread and not exaggerated, then the author's conclusion is strengthened.
Second, the author rules out the possibility of adding a lane to BH by showing the failure of GH. However, to evaluate this argument's soundness, we need to know what exactly caused the traffic conditions in GH to deteriorate. It is very likely that the rise in the population near GH, or the increase in vehicles, rather than the construction of the travel lanes, caused the traffic congestion. Or, it is possible that the new travel lanes in GH actually made it easier for people to get around, thus attracting people who previously did not use GH to start using it, which increased congestion in GH but actually diverted traffic throughout the area. Finally, there is also the possibility that the construction of other roads has forced other vehicles to choose GH, which further increases traffic congestion on GH. If there is evidence that any of these possibilities is true, then the author's conclusion will be weakened. Conversely, the conclusion of the article would be strengthened.
Third, even if it is true that GH is more congested because of the opening of a new lane, we need to know whether GH and BH are analogous. Specifically, we need information concerning the difference regarding the conditions of the two highways themselves. For example, the road conditions of BH and GH may be different. That is to say, GH's road is already wide, then building a new lane would instead only increase congestion. By contrast, BH's roads are narrow, and building a new lane could greatly improve its traffic conditions. If this is the case, the author's conclusion will be challenged. However, any evidence of the similarities between BH and GH would strengthen the article.
Finally, even if it is true that an additional lane should not be built in BH, we need to know the feasibility and effectiveness of the option of building a bike lane. The author mentions that residents enjoy bicycling, but do not tell us whether they would accept bicycle commuting. If there is evidence that residents only treat bicycling as a hobby, but that long bike commutes would be a burden to them, then building bike lanes would not encourage people to bike more, and then the author's proposal would not be feasible. Furthermore, even if bike lanes were feasible, we would need to know whether such a move would actually reduce traffic congestion. If there is evidence that the bicycle lanes are counterproductive, such as the influx of bicycles interfering with road order, then the author's conclusion would still be rejected.
In sum, we need the evidence mentioned above to better evaluate the reasoning of the author's conclusions. Only when we considered all the evidence that may both strengthen and weaken the argument can we determine the validity of the author's conclusion.