Uploaded on 2015-05-13 by sohearn1860

[1]: https://edxuploads.s3.amazonaws.com/14315499534061364.jpg The visible is the traffic lights on the bridge and the traffic crossing the 10km bridge which connects the 2 parts of Maryland (west and east). The invisible are the controls and safeguards against accidents. The maritime traffic into Baltimore also interacts to keep trade lanes open.