Do not escape comma in query parameter using Web.Contents

I need to preserve a comma in a query string value passed to Web.Contents but have been unable to do so successfully.  There's two different instances of using commas in the code below - origins and destinations parameters.   In both cases they are always escaped. 

let 
    DistanceLookup = (SourceLatitude as number,SourceLongitude as number) =>
let   
    Source = Xml.Tables(Web.Contents("http://dev.virtualearth.net/REST/v1/",[
        RelativePath="Routes/DistanceMatrixAsync?origins=" &Text.Trim(Number.ToText(SourceLatitude)) & "," & Text.Trim(Number.ToText(SourceLongitude)),
        Query=
		[		
			destinations="55.55,-55.55",
			travelMode="driving",
			distanceUnit="mi",
            o="xml",
            key="XXXXXX"
		]
    ])),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Copyright", type text}, {"BrandLogoUri", type text}, {"StatusCode", Int64.Type}, {"StatusDescription", type text}, {"AuthenticationResultCode", type text}, {"TraceId", type text}})
in
    #"Changed Type"
in 
    DistanceLookup